Search PubMed⌕ Search

Biomedical subjects

G H Zeilmaker

Publications and source records attributed to G H Zeilmaker.

At least 73 records · Page 4Linked to original sources
PubMed1981

In vitro fertilizing capacity of fresh and cryopreserved human spermatozoa: a comparative study of freezing and thawing procedures.

The capacity of human spermatozoa to penetrate zona-free hamster ova was used to investigate several methods of freezing and thawing sperm. No differences in postthaw sperm viability were obtained after cooling spermatozoa either with a complex egg yolk cryoprotective medium or glycerol. The in vitro fertilizing capacity of postthaw spermatozoa frozen with a moderate freezing rate was similar to that of spermatozoa frozen with a slow freezing rate. Significantly higher in vitro fertilization percentages were found when the spermatozoa were thawed at an environmental temperature of 22 degrees C (mean 51%) or 37 degrees C (mean 52%), as compared with spermatozoa thawed at 4 degrees C (mean 37%). Individual differences of in vitro fertilization percentages are discussed in relation to changes in motility. It is demonstrated that a high prefreeze in vitro fertilization percentage is no guarantee of a high postthaw fertilizing ability.

Animals↗
PubMed1981

Prolonged steroidogenesis in luteinized ovaries of hypophysectomized rats.

Luteinized ovaries of rats hypophysectomized shortly after ovulation 25-80 days previously secrete considerable amounts of 20 alpha-dihydroprogesterone (20 alpha-hydroxy-4-pregnen-3-one, 20 alpha-OHP) into the bloodstream. The serum concentration of 20 alpha-OHP in these hypophysectomized animals is almost similar to that of progesterone in intact pseudopregnant rats on day 7 of pseudopregnancy, in spite of the absence of demonstrable amounts of prolactin. Isolated corpora lutea of the last generation and the remainder of the ovarian tissue both contained 20 alpha-OHP. Six months after hypophysectomy no detectable amount of 20 alpha-OHP was found in the serum. Androgenized rats, devoid of corpora lutea, did not produce 20 alpha-OHP after hypophysectomy. These data show that pituitary hormones are not required for the prolonged synthesis and secretion of 20 alpha-OHP by the luteinized ovary.

20-alpha-Dihydroprogesterone↗
PubMed1980

Diurnal prolactin surges and sexual differentiation of the rat hypothalamus.

Neonatal exposure to testicular androgens interferes with the ability in adulthood to release an ovulatory amount of LH, with the display of female sexual behavior, and also with control mechanisms of the activity of the corpora lutea. It is likely that effects on luteal activity involve, in part, effects on the control of PRL secretion. Therefore, serum concentrations of PRL were studied in ovarian graft-bearing male rats, castrated as neonates (NC-males) or as adults (AC-males), during a luteal phase induced and temporarily sustained by an ectopic pituitary graft. Before the removal of the pituitary graft, serum PRL and progesterone levels were high at all times when measured during the day in both AC-males and NC-males. Removal of the pituitary graft, 6-7 days after ovulation led to immediate cessation of luteal activity in AC-males but not in NC-males. In the latter animals, luteal activity was maintained for at least 6 days after pituitary graft removal by intermittently high levels of PRL, i.e. around 0400 and 1900 h. However, in AC-males, PRL levels were generally low after pituitary graft removal. It is concluded that the absence of neonatal exposure to testicular secretion contributes to the ability of the adult rat to release PRL in a diurnal surge-like manner. The inability to release PRL in this way may explain the failure of AC-males to maintain luteal activity.

Animals↗
PubMed1979

Serum prolactin concentrations during hormonally induced pseudopregnancy in the rat.

Treatment of 5-day cyclic rats with 10 or 100 microgram estradiol benzoate on the day of estrus induced a luteal phase in all animals studied. On the other hand, an injection with 1 microgram estradiol benzoate given on the same day failed to induce pseudopregnancy. When 10 mg progesterone were injected on the day of estrus, about 50% of the rats became pseudopregnant, whereas most of the remaining rats had a 6-day cycle. The injection of 10 or 100 microgram estradiol benzoate or 10 mg progesterone induced a period of increased PRL secretion which lasted for 2--4 days, followed by twice daily surges of PRL at the end of the dark and light periods, respectively. It is argued that pseudopregnancy induction by estradiol benzoate or progesterone is primarily a result of the induction of a period of increased PRL secretion. In this way, progesterone secretion by the recently formed corpora lutea is induced, and the elevated levels of progesterone in turn generate diurnal surges of PRL.

Animals↗
PubMed1979

Ovulation blockade and receptivity in the cyclic rat.

The onset and decline of sexual receptivity was determined around oestrus in intact 5-day cyclic rats and in animals in which spontaneous ovulation was inhibited with nembutal. It was observed that early receptivity (before the critical hours at 14--16 h) could be induced by prior exposure of pro-oestrous females to male rats during the morning at pro-oestrus. In most cases early receptivity was associated with a failure to block ovulation with nembutal administered at 14 h. In cyclic rats receptivity disappeared on the day of oestrus between 8 and 10 a.m. By contrast the period of receptivity was prolonged for 24 h in animals in which ovulation was inhibited by nembutal. Reflex ovulation could be induced by exposure of nembutal-blocked rats to intact as well as to pudendectomized male rats, which latter cannot achieve intromissions. This illustrates the limited role of female genital stimuli in the induction of reflex ovulation. Progesterone (1.25 or 5 mg) injected at pro-oestrus during nembutal sedation did not have an attenuating effect on receptivity 24 h later. It is concluded that LH-surge dependent progesterone secretion at pro-oestrus is not essential for the induction and termination of receptivity around oestrus and that hormones, presumably oestrogens, secreted by the persistent pre-ovulatory follicles, are responsible for the prolonged period of receptivity following nembutal blockade of ovulation.

Animals↗
PubMed1978

Luteotrophic activity of ectopically developing rat blastocysts.

The production of a luteotrophic hormone by ectopically transplanted rat blastocysts was demonstrated by transfer of blastocysts to the kidneys of cyclic and pseudopregnant mice and isogeneic rats. Pseudopregnancy was induced in nearly all cyclic mice bearing trophoblastic outgrowths but not in cyclic rats. In both mice and rats prolongation of pseudopregnancy was observed following ectopic transplantation of rat blastocysts at the time of normal egg implantation. It is concluded that ectopically developing rat trophoblastic tissue produces a luteotrophic hormone.

Animals↗
PubMed1977

Lactate concentrations in pre-ovulatory follicles of pro-oestrous rats before and after onset of oocyte maturation.

Lactate concentrations were determined in pre-ovulatory follicles of rats at pro-oestrus before and after onset of oocyte maturation. It appeared that high concentrations prevail before and after the time of the expected LH surge (27 mM). The level in serum was about 5 mM. Explanted oocytes obtained from pre-puberal rats and surrounded by cumulus cells, matured in the presence of 20 mM lactate as sole exogenous energy source. It is argued that oxygen may be the limiting factor suppressing oocyte maturation in vivo.

Animals↗
PubMed1976

Role of pelvic nerves in the postcopulatory abbreviation of behavioral estrus in female rats.

The role of the pelvic nerves in the postmating abbreviation of behavioral estrus in domestic female rats was investigated. Mating during a period of 40 min at the beginning of hormonally induced estrus in spayed female rats resulted in a rapid decrease in receptivity as measured hourly by the lordosis response. Moreover, the length of the receptive period was significantly shortened by mating at the start of the period. Bilateral pelvic nerve transection completely abolished these effects of mating. Continuous exposure to sexually active males throughout the period of receptivity resulted in a more pronounced decline in receptivity but again was without effect in pelvectomized females. Apparently genital stimuli mediated by the pelvic nerves are responsible for the postcopulatory decrease in receptive behavior in the female rat.

Animals↗