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.

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.

Prolonged release by dioestrous rats of follicle-stimulating hormone during the period of ovulation induced by luteinizing hormone releasing hormone

When 1·0 μg luteinizing hormone releasing hormone (LH-RH) was given i.v. three times at 1 h intervals from 17.00 to 19.00 h on the day of dioestrus (day 0) to regular 4 day cyclic rats, premature ovulation was induced the next morning (day 1) with the number of ova present comparable to normal spontaneous ovulation. The next spontaneous ovulation occurred on the morning of day 5, 4 days after premature ovulation induced by LH-RH.

Plasma concentrations of FSH and LH showed transient rises and falls within 1 h of administration of LH-RH; concentrations of FSH in the plasma decreased from 20.00 h on day 0 but markedly increased again from 23.00 h on day 0 to 02.00 h on day 1 and these high levels persisted until 14.00 h on day 1, with only a small increase of plasma LH during this period. The duration of increased FSH release during premature ovulation induced by LH-RH treatment was 6 h longer than the FSH surge occurring after administration of HCG on day 0. Surges of gonadotrophin were absent on the afternoon of day 1 (the expected day of pro-oestrus) and the surges characteristic of pro-oestrus occurred on the afternoon of day 4 and ovulation followed the next morning. The pituitary content of FSH did not decrease despite persisting high plasma levels of FSH during premature ovulation induced by either LH-RH or HCG on day 0.

The changes in uterine weight indicated that the pattern of oestrogen secretion from the day of premature ovulation induced by LH-RH to the day of the next spontaneous ovulation was similar to that of the normal 4 day oestrous cycle. When 10 i.u. HCG were given on day 0, an increase in oestrogen secretion occurred on day 2, 1 day earlier than in the group given LH-RH on day 0. This advancement of oestrogen secretion was assumed to be responsible for the gonadotrophin surges on day 3.

Similar numbers of fully developed follicles were found by 17.00 h on day 2 after premature ovulation induced by either LH-RH or HCG, suggesting that the shorter surge of FSH during premature ovulation induced by HCG had no serious consequences on the initiation of follicular maturation for the succeeding oestrous cycle in these rats.

Administration of LH-RH on day 0 had no direct effect on the FSH surge during premature ovulation. Secretory changes in the ovary during ovulation may be responsible for this prolonged selective release of FSH.

Selective release of follicle-stimulating hormone during the period of ovulation induced by human chorionic gonadotrophin in dioestrous rats

Laboratory of Veterinary Physiology, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183, Japan

(Received 2 May 1977)

When an amount of human chorionic gonadotrophin (HCG) sufficient to cause ovulation is given to 4-day cyclic rats on the day of dioestrus, premature ovulation is induced the next morning (Eto & Imamichi, 1955). The pattern of release of follicle-stimulating hormone (FSH) responsible for the initiation of follicular maturation of the next set of follicles (Schwartz, 1969; Welschen & Dullaart, 1976) after HCG-induced ovulation has not been previously evaluated. The present communication is concerned with this problem and indicates that a large amount of FSH is released within 12 h of administration of HCG, with only a small concomitant rise in the concentration of luteinizing hormone (LH).

Adult female Wistar rats were maintained under a 14 h light : 10 h darkness schedule (lights on 05.00 h), and those showing three or

Studies on peroxisomes. VI. Relationship between the peroxisomal core and urate oxidase

The peroxisomal core from the liver of rats was purified 450-fold as a marker of urate oxidase [EC 1.7.3.3.] activity. This preparation has a high specific activity of urate oxidase but not of other peroxisomal enzymes: D-amino acid oxidase [EC 1.4.3.3.], L-alpha-hydroxy acid oxidase [EC 1.1.3.15], or catalase [EC 1.11.1.6]. No activity of marker enzymes for other subcellular particles; cytochrome c oxidase [EC1.9.3.1] (mitochondria), acid phosphatase [EC 3.1.3.2] (lysosomes), or glucose-6-phosphatase [EC 3.1.3.9] (microsomes), was detected in this preparation. The core obtained showed a single protein band in sodium dodecyl sulfate-polyacrylamide gel electrophoresis and the position of the band was found to correspond to a molecular weight 35,000. When the peroxisomal core was subjected to treatment at various pH's with 0.1 M carbonate buffer, urate oxidase was almost completely solubulized at pH 11.0, although approximately 35% of the core protein still remained in the pellet After solubilization of the core at pH 11.0, the specific activity of urate oxidase in the supernatant increased about 1.6 times; the density of the insoluble protein remaining in the pellet was identical with the that of the original core on sucrose density gradient centrifugation.

Purification and some properties of NADP+ -specific isocitrate dehydrogenase from an extreme thermophile, Thermus flavus AT-62

Thermostable NADP+ -specific isocitrate dehydrogenase (EC 1.1.1.42) was purified from crude extract of an extremely thermophilic bacterium Thermus flavus AT-62 through DEAE-cellulose column, acetone fractionation, DEAE-Sephadex A-50 column and isoelectric focussing. The enzyme was purified about 500-folds in its specific activity and purity was found to be about 96%. The enzyme was not inactivated after 60 min at 70 degrees C, but 20 and 80% of the activity were lost after 60 min at 80 degrees and 90 degrees C, respectively. Oxalacetate plus glyoxylate (each 1 nM) demonstrated 75% inhibition of the activity in concerted manner. The degree of the inhibition and the affinity of the enzyme for isocitrate and NADP+ decreased with the rise of temperature, especially above 60 degrees C. The activation energy below and above 60 degrees C were 14,500 and 8,000 cal per mole respectively. In CD spectra negative bands at 210 and 220nm were observed and alpha-helix content was calculated to be about 26%. In the course of heating up to 60 degrees practically no change in CD bands are observed, but above 60 degrees the depth of CD bands decreased gradually and remarkably above 80 degrees C. The effect of temperature on kinetic parameters and secondary structures of the enzyme was discussed in relation to the temperature adaptation of the organism.

Effect of prostaglandin F2alpha upon ovulation and LH, FSH and prolactin secretion in chlorpromazine blocked rats

The ovulation-inducing and LH, FSH and protein releasing activities of prostaglandin F2alpha (PG F2alpha) were investigated, using the female rats which had ovulation blocked by chlorpromazine (CPZ). Serum LH, FSH and prolactin concentrations were measured with NIAMD-rat-radioimmunoassay kits. The number of ova present in the fallopian tubes was investigated microscopically. Subcutaneous injection of 0.4-1.6 mg of PG F2alpha at 3:00 p.m. to CPZ-blocked proestrous rats induced ovulation in 80% of the animals during presumptive estrus. However, the percentage of ovulating rats was reduced in 40-60% of the animals when the same doses of PG F2alpha were injected intravenously. All control animals receiving the vehicle alone did not ovulate. The number of ova was not related to the dose of PG F2alpha, but the percentage of ovulating rats was. The serum LH peak was observed 10 min after the intravenous injection and 60-180 min after the subcutaneous injection of PG F2alpha. The peak in serum FSH and prolactin occurred simultaneously 180 min after both subcutaneous and intravenous injection of PG F2alpha. It is concluded from these data that PG F2alpha at dose levels used, may directly affect the hypothalamo-pituitary axis and consequently induce ovulation. These results further support the conception that the prostaglandins (PGs) have a central effect stimulating LH, FSH and prolactin release from the anterior pituitary.

Direct action of prostaglandins on the rat pituitary

The purpose of this study is to ascertain whether or not prostaglandins (PGs) act directly on the pituitary. In the first experiment, the plasma LH levels were sharply decreased 24 hr after the production of hypothalamic lesions in ovariectomized mature rats. Ten min after the iv injection of PGE1, PGE2 or PGF2alpha, the plasma LH levels increased significantly as compared with the vehicle control. Also, the plasma LH levels were elevated following the iv injection of LH-releasing hormone (LH-RH). In the second experiment, after pretreatment of ovariectomized mature rats with estrogen and progesterone, animals received a SC injection of indomethacin, 2 mg in 0.2 ml of gelatin for 3 days. Twenty-four hr after the last injection, 100 ng of LH-RH were injected into the jugular vein. The response of the pituitary to the LH-RH was significantly lower in the indomethacin-treated rats than in the vehicle control rats. In the 3rd experiment, we tested several PGs for stimulatory effects on LH secretion by injecting them into the anterior pituitary. Following direct microinjection of PGE1 or PGE2 (50 or 100 mug/mul) into the rat pituitary, plasma LH was increased at 10 and 45 min after the injection. However, PGF2alpha at both 50 and 100 mug/5mul, failed to increase the plasma LH levels. In the last experiment, the effect of PGE1, PGE2 or PGF2alpha on in vitro rat anterior pituitary LH release was studied. Addition of PGE1, (2 or 20 mug), PGE2 (0.002 or 0.02 mug) or PGF2alpha (200 mug) to the incubation medium produced a significant increase in LH release into the incubation medium. These observations indicate that sufficient dosages of PGs can also stimulate LH secretion by acting directly on the pituitary.