Luteinizing Hormone-Releasing Hormone Release during the Rat Estrous Cycle and after Ovariectomy, as Estimated with Push-Pull Cannulae*
Open Access
- 1 November 1982
- journal article
- research article
- Published by The Endocrine Society in Endocrinology
- Vol. 111 (5), 1439-1448
- https://doi.org/10.1210/endo-111-5-1439
Abstract
A push-pull perfusion (PPP) system was used to carry out the first examination of LHRH release from the mediobasal hypothalami (MBH) of conscious, freely moving rats during stages of the estrous (E) cycle and after ovariectomy (Ovx). Female rats received push-pull cannula (PPC) implants into the MBH and then were allowed to recover for 2–10 weeks before PPP experiments. During that time, E cycles were determined by daily inspection of vaginal smears. After exhibiting two consecutive E cycles, rats were fitted with indwelling jugular catheters between 0830–1030 h and subjected to PPP of the MBH and hourly bleeding for more than 6 h. LHRH and LH levels were determined by RIA in perfusates and plasma, respectively. PPP and bleeding sessions were performed on the afternoon of proestrus (Pro; n – 10), diestrous day I (DI; n – 5), diestrous day II (DII; n – 5), estrus (E; n – 5), or more than 28 days after Ovx (n – 5). LHRH output was detectable in at least some samples in all rats whose PPC tips resided within 0.5 mm of the rostrolateral median eminence. Basal LHRH output (P < 0.01) compared to that in all other groups and was distinctly biphasic; a putative priming pulse (P < 0.05) occurred 2–3 h before the occurrence of a larger main peak (1.6–7.0 pg-12 min) at approximately 1600–1730 h (lights on from 0500–1900 h). Proestrous (Pro) LH levels in rats bearing PPC implants were only 10–30% of those in intact rats regardless of PPP. Nonetheless, these rats did exhibit temporally normal Pro LH surges concident with LHRH release. In DI and DII rats, LHRH pulse amplitude increased moderately for a brief period in the late afternoon (P < 0.01 only when data was normalized to the largest peak). LHRH output in E rats was low and mostly undetectable. Pulse amplitude in ovariectomized (Ovx) rats remained constant and low throughout the afternoon, while LH levels were elevated to typical post-Ovx values. We conclude from this study that (1) a biphasic LHRH surge occurs on the afternoon of Pro which may act to prime and then stimulate pituitary gonadotrophes, (2) small but significant increases in LHRH pulse amplitude occur between 1500–1900 h in DI and DII rats, but not in Ovx or E rats, and (3) LH, but not LHRH, release is increased in Ovx rats, suggesting that the negative feedback effects of ovarian steroids operate primarily at the level of the pituitary gland.Keywords
This publication has 23 references indexed in Scilit:
- Relationship Between Luteinizing Hormone Releasing Hormone Concentration in Hypophysial Portal Blood and Luteinizing Hormone Release in Intact, Castrated, and Electrochemically-Stimulated Rats1Endocrinology, 1977
- Pituitary Stalk Portal Blood Collection in Rhesus Monkeys: Evidence for Pulsatile Release of Gonadotropin-Releasing Hormone (GnRH)Endocrinology, 1976
- Extinction of the Estrogen-Induced Daily Signal for LH Release in the Rat: A Role for the Proestrous Surge of ProgesteroneEndocrinology, 1976
- Surgical Analysis of the Preoptico-Tuberal Pathway Controlling Ovulatory Release of Gonadotropins in the RatEndocrinology, 1967
- Hormone Secretion of the Anterior Pituitary Gland After Physical Interruption of All Nervous Pathways to the Hypophysiotrophic AreaEndocrinology, 1965
- Fluctuations in Hypothalamic LH-RF (Luteinizing Hormone-Releasing Factor) During the Rat Estrous CycleEndocrinology, 1965
- Acute effects of ovariectomy on pituitary LH, uterine weight, and vaginal cornificationAmerican Journal of Physiology-Legacy Content, 1964
- Central Neural Control of Reproductive Functions of the AdenohypophysisPhysiological Reviews, 1964
- THE EFFECT OF ESTROGEN ON PLASMA LUTEINIZING HORMONE (LH) ACTIVITY IN THE RAT1Endocrinology, 1961
- A 24-HOUR PERIODICITY IN THE “LH-RELEASE APPARATUS” OF FEMALE RATS, DISCLOSED BY BARBITURATE SEDATION1Endocrinology, 1950