PLASMA PROLACTIN IN OVARIECTOMIZED RATS C. A. BLAKE
Department ofAnatomy, Duke University Medical Center, Durham, North Carolina 27710, U.S.A.
(Received
15 July
1975)
Radioimmunoassay of luteinizing hormone (LH) in sequential blood samples collected continuously over 2\p=n-\12min periods from ovariectomized (OVX) rats has shown the concentration of LH in blood to fluctuate at high levels in a pulsatile rhythm (Gay & Sheth, 1972). The present study investigates whether plasma prolactin fluctuates regularly at low levels in OVX rats.
Sprague\p=n-\Dawleyrats kept in a room with the lights on from 05.00 to 19.00 h were ovariectomized and used 12\p=n-\16weeks later. A cannula was inserted into the right atrium (Terkel, 1972) before 10.00 h. At this time or 3 days later rats were placed in separate buckets containing food and water. Blood (0\m=.\3ml) was withdrawn through the cannulae and replaced with heparinized saline over a 60 s period at 10 min intervals from 17.00 to 18.00 h or at 10 or 20 min intervals from 17.00 to 19.00 h. Non-cannulated OVX rats were bled into heparinized tubes by decapitation at 17.00 h. Half were stressed by each being placed in a bucket at 10.00 h. The other seven were non-stressed and decapitated immediately after removal from their cages at 17.00h. Five non-stressed rats showing cycles were decapitated at 17.00 h on dioestrus
18.00 17.00 Time of day
Fig.
1. Plasma
prolactin (solid circles) and plasma LH (open circles) concentrations are plotted
at 10 min intervals from 17.00 to 18.00 h for 8 individual rats in which both hormones were
measured in each blood
sample.
1. Plasma LH and prolactin were measured in duplicate in single assays for each hormone described previously (Blake, Scaramuzzi, Norman, Hilliard & Sawyer, 1973). Values are expressed as ng/ml plasma in terms of the NIAMDD standards which have biological potencies equivalent to 0-03 x NIH-S1 and 11 i.u./mg for LH and prolactin, respectively. Voogt & Ganong (1972) found plasma prolactin fluctuated in 15 min blood samples collected continuously over a period of 3 h in OVX rats. Their collection technique which resulted in an integration of hormone concentrations over 15 min periods and the rapid with¬ drawal of samples at 20 min intervals in this study often did not permit detection of a pulsatile rhythm in plasma LH. Regular pulsatile increases in plasma LH were apparent in all rats bled at 10 min intervals but plasma prolactin as measured in the same samples increased and decreased in an erratic, unpredictable manner regardless of whether the rats were cannulated 3 days previously (Fig. 1) or 7—9 h before blood collection. It must be questioned whether these changes in plasma prolactin represent a true index of similar patterns of change that might occur in non-cannulated OVX rats or whether they represent an end result from the 'stress' of the cannula. Plasma prolactin in all groups of OVX rats was lower (P< 0 5; Mest) than in the dioestrous rats (46 ±3-1 (SE.M.) ng/ml) but plasma prolactin in rats cannulated 3 days or 7—9 h before blood collection was higher (P< 0-001) than in stressed and nonstressed decapitated OVX rats (27 ± 2-6 and 28 ± 5-7 v. 11 ± 3-1 and 12 + 3-0, respectively). Heparinization of the cannulated rats cannot account for the increased prolactin levels since these rats were not heparinized before the first blood collection on which the mean plasma prolactin titres were calculated.
day as
This work was
supported by the NIH (HSAA 5 S04 RR06148 and 5 SO1-RR-05404).
Blake, C. ., Scaramuzzi, R. J., Norman,
REFERENCES L., Hilliard, J. & Sawyer, C. H. (1973). Endocrinology 92,
R.
1419-1425.
Gay, V. L. & Sheth, N. A. (1972). Endocrinology 90,158-162. Terkel, J. (1972). Journal of Applied Physiology 33,519-522. Voogt, J. L. & Ganong, W. F. (1972). Abstr. Papers 4th int. Congr. Endocr., Washington, June 1972. ICS. No. 256, pp. 72-73. Amsterdam: Excerpta Medica Foundation.
Department ofAnatomy, Duke University Medical Center, Durham, North Carolina 27710, U.S.A.
(Received
15 July
1975)
Radioimmunoassay of luteinizing hormone (LH) in sequential blood samples collected continuously over 2\p=n-\12min periods from ovariectomized (OVX) rats has shown the concentration of LH in blood to fluctuate at high levels in a pulsatile rhythm (Gay & Sheth, 1972). The present study investigates whether plasma prolactin fluctuates regularly at low levels in OVX rats.
Sprague\p=n-\Dawleyrats kept in a room with the lights on from 05.00 to 19.00 h were ovariectomized and used 12\p=n-\16weeks later. A cannula was inserted into the right atrium (Terkel, 1972) before 10.00 h. At this time or 3 days later rats were placed in separate buckets containing food and water. Blood (0\m=.\3ml) was withdrawn through the cannulae and replaced with heparinized saline over a 60 s period at 10 min intervals from 17.00 to 18.00 h or at 10 or 20 min intervals from 17.00 to 19.00 h. Non-cannulated OVX rats were bled into heparinized tubes by decapitation at 17.00 h. Half were stressed by each being placed in a bucket at 10.00 h. The other seven were non-stressed and decapitated immediately after removal from their cages at 17.00h. Five non-stressed rats showing cycles were decapitated at 17.00 h on dioestrus
18.00 17.00 Time of day
Fig.
1. Plasma
prolactin (solid circles) and plasma LH (open circles) concentrations are plotted
at 10 min intervals from 17.00 to 18.00 h for 8 individual rats in which both hormones were
measured in each blood
sample.
1. Plasma LH and prolactin were measured in duplicate in single assays for each hormone described previously (Blake, Scaramuzzi, Norman, Hilliard & Sawyer, 1973). Values are expressed as ng/ml plasma in terms of the NIAMDD standards which have biological potencies equivalent to 0-03 x NIH-S1 and 11 i.u./mg for LH and prolactin, respectively. Voogt & Ganong (1972) found plasma prolactin fluctuated in 15 min blood samples collected continuously over a period of 3 h in OVX rats. Their collection technique which resulted in an integration of hormone concentrations over 15 min periods and the rapid with¬ drawal of samples at 20 min intervals in this study often did not permit detection of a pulsatile rhythm in plasma LH. Regular pulsatile increases in plasma LH were apparent in all rats bled at 10 min intervals but plasma prolactin as measured in the same samples increased and decreased in an erratic, unpredictable manner regardless of whether the rats were cannulated 3 days previously (Fig. 1) or 7—9 h before blood collection. It must be questioned whether these changes in plasma prolactin represent a true index of similar patterns of change that might occur in non-cannulated OVX rats or whether they represent an end result from the 'stress' of the cannula. Plasma prolactin in all groups of OVX rats was lower (P< 0 5; Mest) than in the dioestrous rats (46 ±3-1 (SE.M.) ng/ml) but plasma prolactin in rats cannulated 3 days or 7—9 h before blood collection was higher (P< 0-001) than in stressed and nonstressed decapitated OVX rats (27 ± 2-6 and 28 ± 5-7 v. 11 ± 3-1 and 12 + 3-0, respectively). Heparinization of the cannulated rats cannot account for the increased prolactin levels since these rats were not heparinized before the first blood collection on which the mean plasma prolactin titres were calculated.
day as
This work was
supported by the NIH (HSAA 5 S04 RR06148 and 5 SO1-RR-05404).
Blake, C. ., Scaramuzzi, R. J., Norman,
REFERENCES L., Hilliard, J. & Sawyer, C. H. (1973). Endocrinology 92,
R.
1419-1425.
Gay, V. L. & Sheth, N. A. (1972). Endocrinology 90,158-162. Terkel, J. (1972). Journal of Applied Physiology 33,519-522. Voogt, J. L. & Ganong, W. F. (1972). Abstr. Papers 4th int. Congr. Endocr., Washington, June 1972. ICS. No. 256, pp. 72-73. Amsterdam: Excerpta Medica Foundation.
