650

Speeialia

Effects of colchicine, lumicolchicine administration and stress loading on NA levels in the LC NA (ng/region) Control Colchicine (50 ~g) Lumieolchicine (400-500 ~xg) Restraint (6h)

18.0 • 0.8(11) 18.2 • 0.7(8) 16.6 ! 0.7(8)

Experimental 29.9 • 1.5(lt)* 17.8 • 0.6(10) 17.5 4- 0.7(8)

Rats were treated with colehicine or lumicolchicine into the lateral ventricles, or put in a wire-meshed cage and immersed in flowing water (15 ~ to the xyphoid process for 6 h. Rats were decapitated 2 days later. Results are expressed as means ~= SE. Numbers of animals are shown in parenthesis. *Denotes the significant difference from controls at the level of 1%.

T h e t i s s u e s for c a t e c h o l a m i n e fluorescence m i c r o s c o p y were p r o c e s s e d b y t h e m e t h o d of F a l c k a n d H i l l a r p is. T h e l u m i c o I c h i c i n e w a s p r e p a r e d f r o m colchieine b y t h e m e t h o d of W i l s o n a n d F r i e d k i n ~9. Results and discussion. N A c o n t e n t s in t h e LC i n c r e a s e d m a r k e d l y 2 d a y s a f t e r colchicine a d m i n i s t r a t i o n (table). D o p a m i n e (DA) c o n t e n t s also i n c r e a s e d s i g n i f i c a n t l y f r o m 2.0 • 0.1 n g t o 3.2 • 0 . 2 n g (N = 4). T h e r e l a t i v e l y low v a l u e s of D A s u g g e s t t h a t t h e r e g i o n d i s s e c t e d as t h e LC h a d negligible c o n t a m i n a t i o n of d o p a m i n e r g i c n e u r o n s , a n d t h e r e f o r e t h e D A a c c u m u l a t e d a f t e r colchicine is t h e o n e localized i n L C as a p r e c u r s o r of NA. C o n s i s t e n t w i t h t h e b i o c h e m i c a l results, t h e h i s t o c h e m i c a l s t u d y d e m o n s t r a t e d t h e m a r k e d a c c u m u l a t i o n of fluorescence in t h e LC (figure). N o t o n l y t h e fluorescence i n t h e cell bodies, b u t also t h a t in t h e a x o n s are m o r e i n t e n s e t h a n t h a t of c o n t r o l , so t h a t t h e a x o n s Call b e m o r e easily recognized. T o see t h e specificity of colchicine action, t h e effect of l u m i c o l c h i c i n e w a s i n v e s t i g a t e d , a n i s o m e r of colchicine, w h i c h h a s a m u c h less m i c r o t u b u l e s b i n d i n g c a p a c i t y a n d is f a r less effective i n b i o c k i n g a x o n a l t r a n s p o r t i n ottler

]~XPERtENTIA 33]5

n e u r o n a l systems20, al. E v e n 10 t i m e s h i g h e r doses of l u m i c o l c h i c i n e t h a n colchicine failed to a l t e r t h e N A levels in t h e LC as well as t h e a n i m a l b e h a v i o r (table). Since t h e i n t r a c i s t e r n a l i n j e c t i o n of colchicine i n d u c e s m a r k e d b e h a v i o r c h a n g e s k n o w n as colchicine n e u r o p a t h y in r a b b i t s 22, we n e x t i n v e s t i g a t e d tile p o s s i b i l i t y t h a t t h i s t r e a t m e n t r e s u l t e d in a g e n e r a l stress, w h i c h in t u r n increased t h e a c t i v i t y of t y r o s i n e h y d r o x y l a s e 1~, t h e r a t e l i m i t i n g e n z y m e of N A s y n t h e s i s , a n d t h u s illcreased t h e N A levels in t h e LC. H o w e v e r , t h e e x p o s u r e of r a t s t o stressful s i t u a t i o n s ( r e s t r a i n t ) failed t o a l t e r t h e N A levels despite increasing the tyrosine hydroxylase activity s i g n i f i c a n t l y f r o m 1.97 • 0.10 to 2.59 • 0.16 n m o l e s D O P A f o r m e d / h region (N : - 8 in e a c h group). T h e morphological evidence available indicates that the intrac i s t e r n a l a d m i n i s t r a t i o n of some a n t i m i t o t i c a g e n t s i n d u c e d a loss of n e u r o t u b u l e s a n d a p r o l i f e r a t i o n of f i l a m e n t s in t h e a n t e r i o r h o r n cells in r a b b i t s ~. Also s i m i l a r b i o c h e m i c a l results t o ours are a v a i l a b l e in w h i c h t h e i n t r a c i s t e r n a l i n j e c t i o n of colchicine m a r k e d l y i n t e r r u p t e d t h e r a p i d m i g r a t i o n of labelled p r o t e i n s in t h e h y p o g l o s s a I a n d v a g u s n e r v e a t t h e level of t h e p e r i k a r y o n 2a. O u r results, t a k e n t o g e t h e r w i t h t h e s e observ a t i o n s , s u g g e s t t h a t t h e b l o c k a d e of a x o n a l t r a n s p o r t is r e s p o n s i b l e for t h e a c c u m u l a t i o n (If N A in t h e LC as a c o n s e q u e n c e of t h e b i n d i n g of colchicine to t h e n e u r o t u b u l e s . H o w e v e r , a f i n a l c o n c l u s i o n is r e s e r v e d u n t i l t h e f a t e of o t h e r i n t r a a x o n a l c o n s t i t u e n t s , s u c h as c a t e c h o l a mine synthetizing enzymes, has been elucidated. A study a l o n g w i t h t h i s line is in p r o g r e s s in o u r l a b o r a t o r y .

18 B. Falck, N. A. Hillarp, G. Thieme and A. Torp, J. Histochem. Cytochem. 10, 348 (1962). 19 L. Wilson and M. Friedkin, Biochemistry 5, 2463 (1966). 20 A. DahlstrSm, P. O. Heiwall and P. A. Larsson, J. Neural Trans. 37, 305 (1975). 21 J.C. Paulson and W. O. McClure, J. Cell Biol. 67, 461 (1975). 22 H. Wisniewski and R. D. Terry, Lab. Invest. 17, 577 (1967). 23 J. Sj6strand, M. Fritzell and P. O. Hasselgren, J. Neurochem. 17, 1563 (1970).

D o p a m i n e b e t a - h y d r o x y l a s e in h u m a n s y n o v i a l fluid M. Sanchez-Martin

and A. G. Garcia i

Departamento de Patologia Quir~rgica and Departamento de Farmacologla, Facultad de Medicina, Valladolid (Spain), 25 November 1976 Summary. D o p a m i n e b e t a - h y d r o x y l a s e ( D B H ) a c t i v i t y h a s b e e n f o u n d i n s y n o v i a l fluid o b t a i n e d f r o m h u m a n knees. T h e e n z y m e a c t i v i t y w a s a b o u t 5 % of t h e a c t i v i t y f o u n d i n t h e s e r u m of t h e s a m e c o n t r o l p a t i e n t s . D B H a c t i v i t y in s y n o v i a l fluid of p a t i e n t s suffering o s t e o a r t h r i t i s was 3 t i m e s h i g h e r . Dopamine beta-hydroxylase (DBH), the enzyme that c a t a l y z e s t h e c o n v e r s i o n of d o p a m i n e t o n o r a d r e n a l i n e (NA) in s y n a p t i c vesicles of s y m p a t h e t i c n e u r o n e s , is released along with NA in response to physiological stimu l a t i o n of adrertergic n e r v e s 3. A c c u m u l a t i o n of D B H in t h e sera of a n i m a l s a n d h u m a n s is n o w well e s t a b l i s h e d ~, 5. Also, tile e n z y m e h a s b e e n d e t e c t e d i n l y m p h fluid of b o t h dogs a n d cats, s u g g e s t i n g t h a t a f t e r s y m p a t h e t i c stimulation the enzyme enters the blood in part through t h e l y m p k ~, 6 Since t h e p r o t e i n c o n t e n t s of h u m a n s y n o v i a l fluid a p p e a r t o b e i d e n t i c a l w i t h t h o s e of p l a s m a 7,

the possibility exists that DBH could also be present in synovial fluid. In this work, D]3H activity was detected in synovial fluid of normal human knees and compared w i t h t h e e n z y m i c a c t i v i t y f o u n d ill s y n o v i a l fluid of p a t h o l o g i c a l j oints.

Material and methods. 19 p a t i e n t s (10 m a l e s a n d 7 females) suffering f r o m n o n j o i n t diseases were selected as controls. Ages r a n g e d b e t w e e n 13 a n d 85 years. I n a d d i t i o n , 12 p a t i e n t s (4 m a l e s a n d 8 females) s u f f e r i n g f r o m osteoa r t h r i t i s ( d e g e n e r a t i v e j o i n t disease) w i t h ages r a n g i n g f r o m 43 t o 63 y e a r s were also s t u d i e d . Of these, 10 p a t i e n t s h a d o s t e o r a r t h r i t i s of t h e k n e e a n d 2 o t h e r p a t i e n t s h a d o s t e o a r t h r i t i s of t h e h i p j o i n t ; 5 were in t h e i n i t i a l stages of t h e disease a n d t h e r e m a i n i n g were in m o r e a d v a n c e d stages. S y n o v i a l fluid of t h e k n e e w a s t a k e n u n d e r g e n e r a l anesthesia from control patients during non-osteoarthritie surgery, a n d f r o m o s t e o a r t h r i t i c p a t i e n t s d u r i n g s u r g e r y of t h e k n e e or t h e h i p joint. E x c e p t for s o m e p a t i e n t s w i t h o s t e o a r t h r i t i s in w h i c h t h e s y n o v i a l fluid w a s t a k e n b y a r t h r o t o m y , f l u i d w a s a l w a y s taken aseptically by paracentesis. Puncture was made

15. 5. 1977

651

Speeialia

Dopamine beta-hydroxylase (DBH) activity in serum and synovial fluid of control and patients with osteoarthritis

Age (years)

Blood pressure (ram Hg) Systolic Diastolic

DBH activity (nmol/h ml) Serum Synovial fluid

S-DBH/SF-DBH

N 17

46.6 ~_ 4.6 (13-85)

131 4. 5 (105-180)

74 i 2.6 (60-90)

245.2 ~_ 42.2 (0-668)

10.9 4- 2.3 (0.4-36)

44.8 4- 18.2 (0-325)

Osteoarthritis 12

55.2 4- 2.1 (43 63)

147 4- 9.6 (90-190)

84 4- 5.2* (60-120)

467.7 4- 101.3" (41-1200)

30.3 4- 7.8** (2.4-102}

18.5 4- 3 (4.1-44)

Control

DBH activity was assayed in t/xl serum and 25 [xl synovial fluid. The optimal pH for the first step ol the reaction was 5; this step was run for 1 h in presence of 10 [xmoles N-ethylmaleimide in order to overcome the effect of endogenous inhibitors. The adequate inactivation of enzyme inhibitors was further tested by adding to a duplicate of each sample a known amount of a partially purified bovine adrenal DBH. With these aliquots of serum and synovial fluid, the recoveries were always greater than 90 %. The activity of a standard amount of partially purified bovine adrenal DBH decreased gradually when aliquots greater than 25 ~1 of synovial fluid were added. However, the enzyme activity was linear with 5-50 ~zl of synovial fluid. Data are means ~ SE. N, number of patients. In parenthesis, range values. SD-BH = Sermn DBH; SF-DBH ~ Synovial fluid DBH. * p < 0.05; ** p < 0.01, compared with controls.

in t h e o u t e r b o r d e r of t h e p a t e l l o - f e m o r a l joint. S y n o v i a l fluid a n d b l o o d o b t a i n e d b y v e n i p u n c t u r e were i m m e d i a t e l y placed in ice-chilled t u b e s a n d c e n t r i f u g e d a t 12,000 • g for 10 rain. T h e s u p e r n a t a n t s f r o m s y n o v i a l fluid a n d s e r u m were frozen a t - 2 0 ~ until a s s a y e d for D B H a c t i v i t y . D B H a c t i v i t y was s t a b l e u n d e r t h e s e c o n d i t i o n s for several weeks. S a m p l e s of s y n o v i a l fluid c o n t a m i n a t e d w i t h blood were discarded. Blood p r e s s u r e s were m e a sured a t t h e t i m e of sampling. T h e m e t h o d e m p l o y e d t o a s s a y D B H a c t i v i t y was slightly m o d i f i e d s f r o m t h a t d e s c r i b e d b y Goldstein e t al. a. Results. The t a b l e s h o w s t h a t s y n o v i a l fluid of c o n t r o l p a t i e n t s c o n t a i n e d a s i g n i f i c a n t a m o u n t of D B H a c t i v i t y , b u t still o n l y 5 ~o t h e a c t i v i t y f o u n d in t h e s e r u m of t h e s a m e p a t i e n t s . The e n z y m e a c t i v i t y was easily m e a s u r e d in s y n o v i a l fluid and, a p p a r e n t l y , t h e e n d o g e n o u s inhibit o r s of t h e e n z y m e were m u c h less p o t e n t w h e n c o m p a r e d to t h o s e p r e s e n t in serum. E v e n t h o u g h t h e r a n g e of v a r i a t i o n of t h e values of D B H a c t i v i t y f o u n d in s y n o v i a l fluid is large, i t was still Smaller t h a n in serum. The t a b l e also s h o w s i n d i v i d u a l s e r u m t o s y n o v i a I fluid D B H ratios ( S - D B H / S F - D B H ) . E x c l u d i n g t h e 2 e x t r e m e v a l u e s (0 a n d 325), it a p p e a r s t h a t ratios m i g h t be m o r e useful in o r d e r to e v a l u a t e c h a n g e s in s y n o v i a l fluid D B H b e t w e e n individuals. P a t i e n t s suffering f r o m d e g e n e r a t i v e j o i n t disease h a d e l e v a t e d s e r u m a n d s y n o v i a l fluid D B H activities. So, while s e r u m D B H a c t i v i t y was a l m o s t t w i c e as m u c h as control, s y n o v i a l fluid D/3H i n c r e a s e d 3 times. Therefore, S - D B H / S F - D B H decreased. Since D B H a c t i v i t y in

IOC

K 6O 4c C3

-= 2( c

0

2o0

400

6o0

8d0

10b0 1100

Serum DBH(nmol/h/ml) The relationship between serum dopamine beta-hydroxylase (DBH) activity and synovial fluid DBH activity in humans. The correlation coefficient was 0.60; p % 0.01; N = 29.

h u m a n s e r u m is a g e - d e p e n d e n t 9, we should c o m p a r e t h e s e d a t a o n l y w i t h c o n t r o l p a t i e n t s w i t h i n t h e s a m e r a n g e of ages. B u t e v e n if p a t i e n t s y o u n g e r t h a n 43 y e a r s are excluded, t h e c o n t r o l g r o u p s e r u m a n d s y n o v i a l fluid D B H values r e m a i n e d similar. Discussion. I t is believed t h a t t h e n o r m a l s y n o v i a l m e m b r a n e e x c l u d e s p l a s m a p r o t e i n s of h i g h m o l e c u l a r w e i g h t 10,11 F o r e x a m p l e , fibrinogen, a p r o t e i n of mol. w t a b o u t 300,000, is n o t f o u n d in n o r m a l s y n o v i a l fluid; t h e r e f o r e it is unlikely t h a t s y n o v i a l fluid D B H , a p r o t e i n of similar mol. w t 12, comes f r o m t h e p l a s m a . The figure s h o w s a p l o t of s e r u m D B H a c t i v i t y v e r s u s s y n o v i a l fluid D B H a c t i v i t y w h i c h reveals t h a t t h e r e is a p o o r b u t significant c o r r e l a t i o n b e t w e e n t h e e n z y m i c a c t i v i t y of b o t h c o m p a r t m e n t s . W h e n t h e s e r u m a n d s y n o v i a l fluid D B H activities were s e p a r a t e l y p l o t t e d for t h e c o n t r o l p o p u l a t i o n a n d for t h e p o p u l a t i o n c o n s i s t i n g of osteoa r t h r i t i c p a t i e n t s , c o r r e l a t i o n c o e f f i e i e n t s o f 0 . 7 9 (p < 0.01) a n d 0.44 (p > 0.05) were o b t a i n e d , respectively. A l t h o u g h poor, t h i s p o s i t i v e c o r r e l a t i o n i n d i c a t e s t h a t if Dt3H in t h e j o i n t does n o t c o m e f r o m t h e p l a s m a , a t least t h e r e is s o m e r e l a t i o n s h i p b e t w e e n t h e D B H activities of b o t h s e r u m a n d s y n o v i a l fluid. On t h e o t h e r h a n d , t h e ratio t o t a l plasm a p r o t e i n / t o t a l s y n o v i a l fluid p r o t e i n is of t h e o r d e r of 2.4 w h i c h is a b o u t 20 t i m e s lower t h a n t h e ratio S - D B H / S F - D B H . Therefore, it has t o be a s s u m e d t h a t t h e s y n o v i a l m e m b r a n e m u s t exclude t h e c i r c u l a t i n g DBI-I o n l y p a r -

1

We thank for the expert technical assistance of Mr Angel Garcia. We are grateful to Drs S. J. Fidone and A. Sillero for assistance with the manuscript. Supported by a grant from the Galerias Preciados Foundation, Valladolid, Spain. 2 A.D. Smith and H. Winkler, in: Catecholamines, p. 538. Ed. H. Blaschko and E. Muscholt. Springer-Verlag, Berlin 1972. 3 M. Goldstein, L. S. Freedman and M. Bonnay, Experientia 27, 632 (1971). 4 R. Weinshilboum and J. Axerold, Circulation Res. 28, 307 (1971). 5 S.H. Ngai, W. Dairman, M. Marehelle and S. Spector, Life Set. ld, 2431 (1974). 6 S . B . Ross, H. E. Eriksson and W. Hellstrom, Aeta physiol. scand. 92, 578 (1974). 7 D. Hamerman, L. C. Rosenberg and M. Schubert, J. Bone Joint Surg. 52-A, 725 (1970). 8 A.G. Garcla and S. M. Kipekar, J. Pharmac. exp. Ther. 792, 343 (1975). 9 L, S. Freedman, T. Ohuehi, M. Goldstein, F. Axerold, I. Fish and J. Dancis, Nature 250, 310 (1972). 10 M. Schubert and D. Hamerman, Bull. rheum. Dis. 14, 345 (1964). I1 D. Hamerman and B. Peter, BuI1. rheum. Dis. 16, 396 (1966). 12 S. Friedman and S. Kaufman, J. biol. Chem. 240, 4763 (1965).

652

Specialia

tlally, or t h a t t h e e n z y m e f o u n d in t h e j o i n t h a s a local source. I t w o u l d b e i n t e r e s t i n g to see if some o t h e r smaller a d r e n e r g i c v e s i c u l a r p r o t e i n s , s u c h as c h r o m o g r a n i n s w h i c h h a v e a tool. w t of 70,000, a n d are also released a l o n g w i t h N A d u r i n g s y m p a t h e t i c n e r v e s t i m u l a t i o n 2, are p r e s e n t in h i g h e r a m o u n t s t h a n DI3H in s y n o v i a l fluid. T h i s w o u l d clarify t h e source of t h e D B H p r e s e n t in s y n o v i a l fluid. L i t t l e is k n o w n a b o u t t h e s y m p a t h e t i c i n n e r v a t i o n

EXPERIENTIA 33/5

of t h e joint, b u t i t m a y b e t h a t t h e e n z y m e c o m e s f r o m sympathetic nerves innervating the joint structures, such as t h e s y n o v i a l m e m b r a n e w h o s e cells h a v e s e c r e t o r y functions. These nerves might regulate the secretory f u n c t i o n s of t h e s e cells, or o t h e r f u n c t i o n s of t h e joints, s u c h as t h e a m o u n t a n d c o m p o s i t i o n of s y n o v i a l fluid, a c r i t i c a l f a c t o r for t h e a d e q u a t e l u b r i c a t i o n of t h e j o i n t cartilage.

I n c r e a s e d c a r d i a c n o r a d r e n a l i n e t u r n o v e r i n t h e r a t a f t e r a c u t e e x p o s u r e to e n v i r o n m e n t a l

heat

R. Sailer a n d B. L e m m e r ~

Ze~trum der Pharmahologie, Theodor-Stern-Kai 7, D-6000 Frank/urt am Main (Federal Republic 5 November 1976

o/Germany, BRD),

Summary. I n m a l e rats, t h e c a r d i a c t u r n o v e r of n o r a d r e n a l i n e is s i g n i f i c a n t l y i n c r e a s e d o n a c u t e e x p o s u r e t o a n e n v i r o n m e n t a l t e m p e r a t u r e of 32 ~ w h e n c o m p a r e d t o c o n t r o l e x p e r i m e n t s p e r f o r m e d a t 23 ~ Various environmental factors influence the metabolism a n d t h 6 t u r n o v e r of n o r a d r e n a l i n e ill t h e r a t h e a r t , e.g. g r o u p i n g of t h e a n i m a l s 2, s t a t e of t r a i n i n g 3, l i g h t a n d d a r k n e s s ~, h i g h a l t i t u d e i n f l u e n c e 5 a n d v a r i o u s f a c t o r s w h i c h are s t r e s s i n g t h e a n i m a l s s. F u r t h e r m o r e , a c u t e a n d l o n g - t e r m e x p o s u r e t o cold increase t h e c a r d i a c n o r a d r e n aline t u r n o v e r in r a t s 7, a n d e n v i r o n m e n t a l h e a t increases t h e n o r a d r e n a l i n e t u r n o v e r ill t h e h y p o t h a l a m u s a, w h i c h p l a y s a n i m p o r t a n t role in t h e t h e r m o r e g u l a t i o n in t h e r a t s, a n d in o t h e r a r e a s of t h e r a t b r a i n 9. As t h e c a r d i a c o u t p u t a n d t h e h e a r t r a t e was r e p o r t e d to b e i n c r e a s e d a t a n e l e v a t e d r o o m t e m p e r a t u r e ~~ i t w a s t h e a i m of t h i s s t u d y to i n v e s t i g a t e w h e t h e r t h e s e c h a n g e s m a y in t u r n b e d u e to an i n c r e a s e d t u r n o v e r r a t e of t h e physiological t r a n s m i t t e r s u b s t a n c e , n o r a d r e n a l i n e , in t h e r a t h e a r t . Materials and methods. I n t h e e x p e r i m e n t s , m a l e W i s t a r r a t s (TNO W.70) o f ' a b o u t 130-160 g were used. T h e anim a l s were k e p t for a t l e a s t 5 d a y s u n d e r a c o n t r o l l e d l i g h t i n g s c h e d u t e of 12 h l i g h t (7.00-19.00 h) a l t e r n a t i n g w i t h 12 h d a r k n e s s (19.00-7.00 h) w i t h food a n d w a t e r a d l i b i t u m a n d a t a r o o m t e m p e r a t u r e of 23 :~ 1~ T h e nora d r e n a l i n e t u r n o v e r in t h e h e a r t s was d e t e r m i n e d in t h e p e r i o d of l i g h t f r o m t h e l o g a r i t h m i c decline of t h e specific

= 100. 80-

tl/z 23~ =14.6h •

t~/2 32~ =8.5h

40-

"~ "6o~ ca

'>-~

20.

L. 19h 3H_NA Clock time

Decay of the specific activity of noradrenaline in the rat heart after i.v. injection of 10 IxCi]kg 3 H-(-)-noradrenaline in the period of light at a room temperature of 23~ ( 9169 or 32~ (e--o). Arrow indicates time of injection at 8.30 h (zero time). Each point represents the mean value ~ SEM from 5 animals.

a c t i v i t y a f t e r i.v. i n j e c t i o n of 10 ~Ci/kg 3 H - ( - ) - n o r a d r e n Mine ( R a d i o c h e m i c a l Centre, A m e r s h a m , spec. a c t i v i t y 8.7 Ci/mmole) as d e s c r i b e d in d e t a i l p r e v i o u s l y *. T h e n o r a d r e n a l i n e c o n c e n t r a t i o n was d e t e r m i n e d a c c o r d i n g t o C h a n g 11. H e a t e x p e r i m e n t s were p e r f o r m e d a t a r o o m t e m p e r a t u r e of 32 • 1~ a n d in o r d e r to a c h i e v e t h i s t e m p e r a t u r e t h e u s u a l e n v i r o n m e n t of t h e a n i m a l s was h e a t e d u p f r o m 7.00 h u n t i l t h e b e g i n n i n g of t h e experim e n t a t 8.30 h. C o n t r o l e x p e r i m e n t s were p e r f o r m e d in t h e s a m e w e e k a t a n o r m a l r o o m t e m p e r a t u r e of 23 • 1 ~ Significance was t e s t e d b y t h e u n p a i r e d 2-tailed S t u d e n t ' s t - t e s t , a n d l i n e a r i t y of t h e regression f u n c t i o n s was p r o v e d by the F-distribution. Results. T h e e n d o g e n o u s n o r a d r e n a l i n e c o n c e n t r a t i o n in t h e h e a r t s was i n c r e a s e d b y t h e a c u t e e x p o s u r e t o h e a t f r o m 0.94 & 0.02 t~g • g-1 (n = 43) a t a n o r m a l t e m p e r a t u r e to 1.04 i 0.02 t x g • -1 (n ~ 43). T h i s increase was s t a t i s t i c a l l y s i g n i f i c a n t (p < 0.001). I n t h e figure, one repres e n t a t i v e e x p e r i m e n t o u t of e a c h e x p e r i m e n t a l g r o u p is depicted, s h o w i n g t h a t t h e half-life of t h e specific a c t i v i t y of t h e c a r d i a c n o r a d r e n a l i n e is d e c r e a s e d w h e n t h e e n v i r o n m e n t a l t e m p e r a t u r e is i n c r e a s e d f r o m 23~ t o 32~ All e x p e r i m e n t a l r e s u l t s are s u m m a r i z e d i n t h e t a b l e . I t c a n b e seen t h a t a c u t e e x p o s u r e t o a n e l e v a t e d r o o m t e m p e r a t u r e of 32~ d u r i n g l i g h t s i g n i f i c a n t l y i n c r e a s e d t h e t u r n o v e r r a t e of n o r a d r e n a l i n e in t h e r a t h e a r t (0.069 ~g • g-1 • h-~) w h e n c o m p a r e d w i t h t h e c o n t r o l e x p e r i m e n t s p e r f o r m e d a t a r o o m t e m p e r a t u r e of 23~ (0.039 txg • g - ~ • h - l ) . T h u s , t h e m e a n half-life was decreased t o 10.2 h a t 32~C f r o m 16.3 h a t 23~ 1

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