The
University
Department of Anatomy, of Texas Health Science Center at San Antonio, San Antonio, Texas 78284, USA
CHANGES IN PITUITARY PROLACTIN LEVELS OF FEMALE HAMSTERS AS A FUNCTION OF AGE, PHOTOPERIOD, AND PINEALECTOMY
By Russel
J. Reiter
ABSTRACT
Exposure of intact female hamsters to light:dark cycles of 1 h light alternating with 23 h darkness (LD 1:23) led to involution of the reproductive organs, a drop in prolactin levels within the anterior pituitary gland, and hypertrophy of the intrascapular brown fat. All of these changes were prevented if the animals were pinealectomized. Pituitary prolactin levels in control hamsters maintained in LD 14:10 cycles also decreased during the 8 week experimental period. Pituitaries of hamsters killed at the end of the experiment contained about four-fifths less prolactin than those necropsied at the beginning of the study.
The synthesis and the secretion of the pituitary gonadotrophins, luteinizing hormone and follicle stimulating hormone, and prolactin are believed to be under the control of certain hypothalamic hypophyseotrophic hormones, the so-called releasing or inhibiting hormones (McCann &- Dhariwal 1966; Blackwell Sc Guillemin 1973; Schally et al. 1973). The hypothalamic humoral envoys responsible for the regulation of the gonadotrophins are generally considered to be stimulatory to LH and FSH synthesis and secretion. These stimulatory factors have been designated LH-releasing hormone and FSH-releasing hor¬ mone. Unlike the gonadotrophins, pituitary prolactin seems to be regulated primarily by an inhibitory substance from the hypothalamus, prolactin releaseinhibiting hormone (PRIH) (Schally et al. 1973). Additionally, a modicum of evidence hints at the existence of a second hypothalamic principle which regu-
lates
prolactin, namely, prolactin releasing hormone
or
PRH
(Nicoli
et
al.
1970). It
likely that the releasing and inhibiting hormones are formed in located either within or near the medial basal hypothalamus. Other portions of the central nervous system, anatomically far removed from the medial basal hypothalamus, undoubtedly are involved in the control of the anterior pituitary gland by acting on the neurons which either form or in¬ fluence the release of the hypothalamic hypophyseotrophic hormones. For example, the preoptic area, the septal area, the limbic system and the reticular formation of the brain stem exert a strong regulatory influence on the neuroendocrine-gonadal axis. Paramount in this hierarchy of control systems is the pineal gland, an organ that can exert profound influences on the gonado¬ trophins and on prolactin. The following report deals with the influence of the pineal gland on reproductive organ weights, as indicators of LH and FSH secretion, and on immunoreactive prolactin levels in female hamsters. seems
neurons
METHODS A total of 87 female golden hamsters (Mcsocricetus auratus, strain LVG:LAK pur¬ chased from Lakeview Hamster Colony, Newfield, New Jersey) were used. The ani¬ mals were 12-13 weeks of age at the onset of the study. Roughly one-half of the animals were pinealectomized 3 weeks before the first animals were necropsied; the remaining animals were left unoperated. The pinealectomy technique of Hoffman 8c Reiter (1965 ) was utilized. For the operation the animals were anaesthesized with sodium pentobarbital. For the first 3 weeks following pinealectomy, all hamsters were kept in long daily photoperiods (light:dark cycles of 14 h light alternating with 10 h darkness; LD 14:10). Thereafter, the animals were maintained either in long (LD 14:10) or short (LD 1:23) daily photoperiods. LD 1:23 cycles were selected since short daily photoperiods have been shown to stimulate the antigonadotrophic activity of the pineal gland in the golden hamster (Hoffman 8· Reiter 1965b; Reiter 8c Hester 1966). The animals were kept in temperature controlled (22 ± 2CC) rooms and were given food and water ad libitum. A group of intact and pinealectomized hamsters was killed at the beginning of the study (after 3 weeks exposure to LD 14:10): thereafter, groups were necropsied after 10, 30 and 56 days of exposure to LD 1:23 cycles. Some animals were maintained in LD 14:10 cycles throughout the experiment. At necropsy, trunk blood samples were collected in heparinized tubes and body weights and weights of the ovaries, uteri and anterior pituitary glands were recorded. Also, because of the appearance of a paper (Heldmaier 8c Hoffmann 1974) during the course of the present study which reported that melatonin (a pineal substance) stimulated growth of brown adipose tissue, the intrascapular brown fat was weighed at the final two necropsy periods. Anterior pituitary glands were homogenized and, with plasma samples, were stored at -20°C. The pituitary and plasma samples were assayed for immunoreactive prolactin using the technique of Donofrio et al. (1973/74) with the aid of radioimmunoassay kits pro¬ vided by the National Institutes of Arthritis and Metabolic Diseases, NIH. Prolactin
bo O
•S 25
M
bo
-G
e
+1
"3
.
S
-H
+1
+1
o
o
+1
+1
co
«^ bo
S-ß Tj
U
H,
f O!
bo P
o
o
o
o
o
+1 +1 +1 4-1 -H +1 c
a
+1
en
o
o
o
tj
4-1
O
ce
ce
co —
—·
*fì —
OOOO
co
o
o
OOOO
+1 +1 +1 +1 4-1 +1 +1 -H +1 +1
o
o
=:
TP
CM
O CM
^h
·**
University
Department of Anatomy, of Texas Health Science Center at San Antonio, San Antonio, Texas 78284, USA
CHANGES IN PITUITARY PROLACTIN LEVELS OF FEMALE HAMSTERS AS A FUNCTION OF AGE, PHOTOPERIOD, AND PINEALECTOMY
By Russel
J. Reiter
ABSTRACT
Exposure of intact female hamsters to light:dark cycles of 1 h light alternating with 23 h darkness (LD 1:23) led to involution of the reproductive organs, a drop in prolactin levels within the anterior pituitary gland, and hypertrophy of the intrascapular brown fat. All of these changes were prevented if the animals were pinealectomized. Pituitary prolactin levels in control hamsters maintained in LD 14:10 cycles also decreased during the 8 week experimental period. Pituitaries of hamsters killed at the end of the experiment contained about four-fifths less prolactin than those necropsied at the beginning of the study.
The synthesis and the secretion of the pituitary gonadotrophins, luteinizing hormone and follicle stimulating hormone, and prolactin are believed to be under the control of certain hypothalamic hypophyseotrophic hormones, the so-called releasing or inhibiting hormones (McCann &- Dhariwal 1966; Blackwell Sc Guillemin 1973; Schally et al. 1973). The hypothalamic humoral envoys responsible for the regulation of the gonadotrophins are generally considered to be stimulatory to LH and FSH synthesis and secretion. These stimulatory factors have been designated LH-releasing hormone and FSH-releasing hor¬ mone. Unlike the gonadotrophins, pituitary prolactin seems to be regulated primarily by an inhibitory substance from the hypothalamus, prolactin releaseinhibiting hormone (PRIH) (Schally et al. 1973). Additionally, a modicum of evidence hints at the existence of a second hypothalamic principle which regu-
lates
prolactin, namely, prolactin releasing hormone
or
PRH
(Nicoli
et
al.
1970). It
likely that the releasing and inhibiting hormones are formed in located either within or near the medial basal hypothalamus. Other portions of the central nervous system, anatomically far removed from the medial basal hypothalamus, undoubtedly are involved in the control of the anterior pituitary gland by acting on the neurons which either form or in¬ fluence the release of the hypothalamic hypophyseotrophic hormones. For example, the preoptic area, the septal area, the limbic system and the reticular formation of the brain stem exert a strong regulatory influence on the neuroendocrine-gonadal axis. Paramount in this hierarchy of control systems is the pineal gland, an organ that can exert profound influences on the gonado¬ trophins and on prolactin. The following report deals with the influence of the pineal gland on reproductive organ weights, as indicators of LH and FSH secretion, and on immunoreactive prolactin levels in female hamsters. seems
neurons
METHODS A total of 87 female golden hamsters (Mcsocricetus auratus, strain LVG:LAK pur¬ chased from Lakeview Hamster Colony, Newfield, New Jersey) were used. The ani¬ mals were 12-13 weeks of age at the onset of the study. Roughly one-half of the animals were pinealectomized 3 weeks before the first animals were necropsied; the remaining animals were left unoperated. The pinealectomy technique of Hoffman 8c Reiter (1965 ) was utilized. For the operation the animals were anaesthesized with sodium pentobarbital. For the first 3 weeks following pinealectomy, all hamsters were kept in long daily photoperiods (light:dark cycles of 14 h light alternating with 10 h darkness; LD 14:10). Thereafter, the animals were maintained either in long (LD 14:10) or short (LD 1:23) daily photoperiods. LD 1:23 cycles were selected since short daily photoperiods have been shown to stimulate the antigonadotrophic activity of the pineal gland in the golden hamster (Hoffman 8· Reiter 1965b; Reiter 8c Hester 1966). The animals were kept in temperature controlled (22 ± 2CC) rooms and were given food and water ad libitum. A group of intact and pinealectomized hamsters was killed at the beginning of the study (after 3 weeks exposure to LD 14:10): thereafter, groups were necropsied after 10, 30 and 56 days of exposure to LD 1:23 cycles. Some animals were maintained in LD 14:10 cycles throughout the experiment. At necropsy, trunk blood samples were collected in heparinized tubes and body weights and weights of the ovaries, uteri and anterior pituitary glands were recorded. Also, because of the appearance of a paper (Heldmaier 8c Hoffmann 1974) during the course of the present study which reported that melatonin (a pineal substance) stimulated growth of brown adipose tissue, the intrascapular brown fat was weighed at the final two necropsy periods. Anterior pituitary glands were homogenized and, with plasma samples, were stored at -20°C. The pituitary and plasma samples were assayed for immunoreactive prolactin using the technique of Donofrio et al. (1973/74) with the aid of radioimmunoassay kits pro¬ vided by the National Institutes of Arthritis and Metabolic Diseases, NIH. Prolactin
bo O
•S 25
M
bo
-G
e
+1
"3
.
S
-H
+1
+1
o
o
+1
+1
co
«^ bo
S-ß Tj
U
H,
f O!
bo P
o
o
o
o
o
+1 +1 +1 4-1 -H +1 c
a
+1
en
o
o
o
tj
4-1
O
ce
ce
co —
—·
*fì —
OOOO
co
o
o
OOOO
+1 +1 +1 +1 4-1 +1 +1 -H +1 +1
o
o
=:
TP
CM
O CM
^h
·**
