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S Sasamoto

Publications and source records attributed to S Sasamoto.

At least 91 records · Page 5Linked to original sources
PubMed1981

Absence of prolactin surge during the period of premature ovulation induced by human chorionic gonadotropin or luteinizing hormone releasing hormone in diestrous rats.

The concentration of plasma prolactin during the period of premature ovulation induced by human chorionic gonadotropin (HCG) or luteinizing hormone releasing hormone (LH-RH) in diestrous rats was determined at 3 hr intervals from 1700 hr on the day of diestrus (day 0) to 2300 hr on the day of proestrus (day 1). Premature ovulation was induced by either a single injection of 10 IU HCG at 1700 hr on day 0 or three injections of 1 microgram LH-RH at 1 hr intervals from 1700 to 1900 hr on day 0. In saline-treated controls, the concentration of prolactin in plasma was low during diestrus but increased on the afternoon of proestrus with a peak value at 1700 hr, followed by an abrupt decline at 2300 hr on the same day. However, there was no significant rise in the plasma prolactin level throughout the period of observation in HCG-treated rats. In the LH-RH treated group, the prolactin level in plasma did not change until 1100 hr on day 1, but significantly increased at 1400 hr on the same day then declined by 2300 hr, though no significant difference was observed at any time when compared to HCG-treated rats. These results indicate that no prolactin surge occurred during the period of premature ovulation.

Animals↗
PubMed1981

Pituitary function during pseudopregnancy and lactation in the rat.

Plasma concentrations of FSH on Days 1, 2, 3, 8 and 9 of lactation (day of parturition = Day 0) were significantly higher than on the corresponding day of pseudopregnancy (day of vaginal plug = Day 1). Pituitary FSH content on Days 4-12 of lactation was also significantly higher than in pseudopregnant rats. However, pituitary LH content on Days 2-12 of lactation was significantly lower than in pseudopregnancy, whereas plasma concentrations of LH were almost similar. Two consecutive injections of LH-RH (100 ng/rat, i.v.), 60 min apart, resulted in a significant release of FSH in lactating rats (Days 3 and 15) in response to the second injection of LH-RH, but there was no increase in pseudopregnant rats on Day 3. The first and second injections of LH-RH produced significantly less release of LH on Days 3 and 15 of lactation than on Day 3 of pseudopregnancy. These results indicate that FSH secretion is not suppressed by suckling whereas the suckling stimulus is a potent inhibitor of LH.

Animals↗
PubMed1981

Delay of the selective surge of follicle-stimulating hormone by bovine follicular fluid during the period of ovulation induced by human chorionic gonadotrophin in dioestrous rats.

When bovine follicular fluid (BFF) was given i.p. three times at intervals of 3 h from 17.00 to 23.00 h to dioestrous rats pretreated with 10 i.u. human chorionic gonadotrophin (HCG) at 17.00 h on the day of dioestrus (day 0), the selective surge of FSH at 02.00 h on day 1 was suppressed in a dose-dependent manner. Three i.p. injections of 0.5 ml BFF completely suppressed the FSH rise in plasma at 02.00 h on day 1, but the time of premature ovulation induced by HCG was not altered. In these animals treated with HCG and BFF, however, the selective surge of FSH occurred as a delayed surge from 05.00 to 23.00 h on day 1. After seven i.p. injections of 0.5 ml BFF (from 17.00 h on day 0 to 11.00 h on day 1) the delayed surge of FSH took place from 17.00 h on day 1 to 11.00 h on day 2, indicating that waning of BFF with a decrease in inhibin secretion by the ovaries may be responsible for the delay of the FSH surge. The next spontaneous ovulation in rats treated with HCG and BFF occurred on day 5, a delay of ovulation of 1 day compared with animals given HCG on day 0 with no BFF. Initiation of follicular maturation or selection of growing follicles for the succeeding oestrous cycle appeared to be retarded by the delay of the FSH surge in HCG- and BFF-treated animals. The pituitary content of FSH in animals given HCG and three i.p. injections of 0.5 ml BFF increased strikingly until 11.00 h on day 1, when the delayed FSH surge was already in progress. These results suggest that the ability of the pituitary gland to synthesize FSH is high during the period of ovulation.

Animals↗
PubMed1980

Mechanism of the selective surge of follicle-stimulating hormone in dioestrous rats during the induction of ovulation by human chorionic gonadotrophin.

A selective surge of FSH with a small concomitant rise in LH occurred invariably in rats when ovulation was induced by injecting human chorionic gonadtrophin (HCG) at various reproductive stages such as day 15 of lactation and in 29-day-old immature rats as well as in dioestrous animals. No FSH surge occurred on day 3 of lactation or in 26-day-old immature rats in which ovulation could not be induced by HCG. The FSH surge occurred 6-18 h after HCG treatment regardless of the time of day of injection of HCG. Ovulation began by 12 h and was completed by 18 h after injection of HCG. Pituitary responsiveness to luteinizing hormone releasing hormone (LH-RH) with respect to FSH release strikingly incresed at 01.00 h on day 1 after HCG injection at 17.00 h of dioestrus (day 0) to levels similar to those of the group at 01.00 h of oestrus, when the greatest response was noted during the normal cycle. With regard to LH release pituitary responsiveness to LH-RH at 01.00 h on day 1 markedly increased but the response was only about half of the response at 01.00 h of oestrus and one third of the response at 17.00 h of pro-oestrus when the greatest response was noted during the normal oestrous cycle. These results indicate that during ovulation the pituitary gland of the rat is highly responsive to LH-RH with respect to the release of FSH, for which secretory changes in the ovary after an ovulating dose of HCG may be responsible.

Animals↗
PubMed1980

Progesterone levels after induction of ovulation in dioestrous rats.

Maximal levels of progesterone in the plasma after premature ovulation induced by either the administration of human chorionic gonadotrophin (HCG) or LH-releasing hormone (LH-RH) to dioestrous (day 0) rats were observed from 33 to 45 h/but/decreased/3 h earlier than after spontaneous ovulation. This suggested an earlier decline in the secretory activity of corpora lutea formed from premature ovulations than that of corpora lutea formed during a normal oestrous cycle. The next spontaneous ovulation occurred 4 days (day 5) after premature ovulation induced by LH-RH on day 0. A single s.c. injection of 2.5 microgram oestradiol-17 beta (OE2) at 10.00 h on day 2 to these animals advanced the next spontaneous ovulation by 1 day. A normal number of oocytes was shed, indicating that earlier secretion of oestrogen on day 2 had advanced the next spontaneous ovulation. A single injection of 2.5 microgram OE2 to normal 4-day cyclic rats at metoestrus failed to advance the next ovulation. An earlier decline of progesterone levels in the plasma of rats after premature ovulation as compared with spontaneous ovulation may explain the greater effectiveness of oestrogen in the former group. The progesterone surge was observed during the period of premature ovulation in both HCG- and LH-RH-treated groups. This progesterone release in the periovulatory period may be responsible for the inhibition of gonadotrophin surges on the expected day of proestrus (day 1).

Animals↗
PubMed1980

Initiation of follicular maturation and ovulation after removal of the litter from the lactating rat.

In order to elucidate the mechanism of the resumption of follicular activity and ovulation in rats, levels of FSH, LH and prolactin in plasma and pituitary gland and ovarian follicular development were quantified after removal of the litter on day 3 of lactation (day of parturition = day 0 of lactation). Such removal resulted in ovulation of 13 oocytes 4 days later, a number comparable with that found in normal cyclic rats. Plasma levels of prolactin were high during lactation but markedly decreased after removal of the litter. Although plasma concentrations of FSH and LH did not change during days 3-7 of lactation, there was an FSH surge between 24 and 30 h after removal of the litter. Plasma concentrations of LH also increased slightly but significantly by 24 h after removal of the litter and this value persisted during the following 2 days. Surges of FSH, LH and prolactin occurred at 17.00 h 3 days after pups were removed. Removal of the litter did not increase pituitary contents of FSH, LH and prolactin and a marked reduction in pituitary levels of FSH and LH, but not of prolactin, occurred at 17.00 h 3 days after removal of the litter. A quantitative study of follicular development indicated that follicles larger than 401 micrometers in diameter were absent during days 3-7 of lactation. However, the number and size of antral follicles increased by 30 h after removal of the litter, probably due to the increases in plasma levels of FSH and LH, and follicles larger than 601 micrometers in diameter appeared 3 days after the young were removed. Although ovulation could not be induced by human chorionic gonadotrophin from days 3 to 5 of lactation, its administration 30 h after removal of the litter produced ovulation in all rats by the following morning. These results indicated that a moderate increase in FSH, although below the amounts released at the preovulatory surge, together with basal levels of LH which were within the range observed on the day of dioestrus during the normal cycle were responsible for the initiation of follicular maturation after removal of the litter.

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