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Luteinizing hormone-releasing hormone in peripheral plasma and hypothalamus of normal and ovariectomized rats.

Abstract：

:Plasma and hypothalamic LHRH was measured by specific radioimmuno-assay in intact and ovariectomized rats, and the values were correlated with peripheral plasma (PP) FSH and LH titers. At most stages of the estrous cycle, plasma LHRH was either undetectable or present at very minimal values. An increase in PP LHRH concentration was observed in some animals between 13.00 and 20.00 h on proestrus. The mean elevation in LHRH was greatest in rats when blood samples were taken by decapitation; elevation was somewhat less when samples were taken from etherized rats and minimal when taken from rats bearing indwelling jugular cannulae. LHRH was elevated in approximately half the ovariectomized animals; repeated samples were drawn at 15-min intervals from intrajugular cannulae. In animals with LHRH elevations, LHRH was highly variable, which indicates that it is released in pulsatile fashion. Plasma LHRH and LH titers were correlated in ovariectomized animals. The relatively low correlation between LHRH and LH may be explained by the fact that a pulse of LHRH can elicit LH release over a considerable time span; also, LHRH is cleared much more rapidly from the circulation than is LH, as revealed by the time course of disappearance of exogenous LHRH given by bolus injection. In intact rats, hypothalamic LHRH content was slightly lower at 10.00 h on diestrus day 1 than at other sample times. LHRH was significantly lower 4 weeks following ovariectomy compared to levels in intact rats at any sample time. It would appear that LHRH's resynthesis does not keep pace with its release in ovariectomized rats, resulting in a decline in hypothalamic stores. :Levels of luteinizing hormone-releasing hormone (LH-RH) in plasma and the hypothalamus were determined by specific radioimmunoassay in int act and ovariectomized rats during the estrous cycle, and the findings stimulating hormone (FSH) and LH. Between 13.00-20.00 hours on the day of proestrus, some animals showed an increased concentration of PP LH-RH. The mean increase in LH-RH values was greatest in samples obtain ed by decapitation, somewhat less in etherized animals, and minimal in s amples obtained from an indwelling jugular cannula. About 50% of the ov ariectomized rats showed elevated levels of LH-RH, though these increases were highly variable. This indicates that LH-RH is released in a pulsatile manner. There was a relatively low correlation between plasma LH and LH-RH titers, which may be explained by the prolonged release of LH after a pulse release of LH-RH, and also by the rapid clearance of LH-RH from circulation. The hypothalamic content of LH-RH was slightly lower at 10.00 hours on the 1st day of diestrus than at other sampling times. Ovariectomized rats had markedly lower hypothalamic levels of LH-RH 4 weeks after ovariectomy than found in intact animals at any sampling period. The results suggest that the resynthesis of LH-RH in ovariectomized rats does not keep pace with its release.

journal_name

Neuroendocrinology

journal_title

Neuroendocrinology

authors

Wheaton JE,McCann SM

doi

10.1159/000122496

subject

Has Abstract

pub_date

1976-01-01 00:00:00

pages

296-310

issue

eissn

0028-3835

issn

1423-0194

journal_volume

pub_type

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Luteinizing hormone-releasing hormone in peripheral plasma and hypothalamus of normal and ovariectomized rats.