Late fetal development and selective resorption in Saccostomus campestris (cricetidae).

When female Saccostomus campestris are stressed during pregnancy they may resorb part of the litter. Resorption can take place on more than one occasion during the same pregnancy without affecting the development of the rest of the litter. The last resorption may be initiated as late as 72-48 h before parturition. No other rodents with a similar gestation appear to resorb at this stage. Resorbing fetuses are isolated within uterine compartments from viable fetuses. Ossification occurs at a comparatively late stage of pregnancy in Saccostomus campestris, and there is a lag-period in fetal growth exactly 72-48 h before parturition. These factors may facilitate late resorption in this species. Factors that may cause stress in this species are most likely environmental; in the present study, dipping of the animal colony to treat for a mite infestation may have induced resorption in some of the females.

Changes in androgen concentrations during puberty and their relation to behaviour in male Saccostomus campestris (Gray 1844), an African rodent.

Sexual development in male Saccostomus campestris, the pouched mouse, was studied in terms of morphological development and changes in concentrations of plasma testosterone and androstenedione. The interaction of adult females and males following the introduction of a male was observed at all stages of the oestrous cycle. The histology of the reproductive organs is similar to that of other rodents. Measurements of the diameter of the seminiferous tubules and the width of the seminiferous epithelium suggest asymptotic growth but, although the diameter had not reached the asymptote at 70 days of age the epithelial width was close to the calculated asymptote at 55 days of age. Intraindividual variation was no greater than variation between individuals of the same age from 55-70 days. Spermatids were not seen in any animals younger than 45 days, but all animals over 55 days of age had spermatozoa in the epididymis. By 70 days of age, fertile matings were observed. At this stage, the seminiferous tubule diameter was still increasing slowly but plasma concentrations of testosterone and androstenedione had reached adult levels; at no time was the concentration of testosterone greater than androstenedione. The males were never aggressive towards females; however, they were severely attacked by females at all stages of the oestrous cycle except pro-oestrus. Only rarely did males show aggression to other males.

Regulation of corpus luteum function in the pouched mouse, Saccostomus campestris.

Regulation of corpus luteum function was studied in pouched mice, housed under controlled conditions (14L:10D), (22 +/- 2 degrees C). Prolactin in daily doses of 32 IU promoted luteal and uterine development and markedly increased plasma levels of progesterone in females exhibiting estrous cycles. Negligible levels of progesterone in prolactin-treated ovariectomized females ruled out the possibility of a significant nonovarian source of progesterone. Domperidone (a dopamine antagonist) induced pseudopregnancy in cycling females, with a marked increase of peripheral progesterone levels. Pseudopregnancy was also induced by artificial vaginal stimulation of cycling females according to a multiple intromission-multiple ejaculation pattern or a shorter, more concentrated stimulation pattern. The latter treatment, however, resulted in a much weaker histological response of the corpora lutea and uterine horns, although plasma levels of progesterone were similar in the two treatment groups. Recently mated females given domperidone daily did not have progesterone levels above those of mated females treated with vehicle only (both groups pregnant). Bromocriptine (a dopamine agonist) prevented newly mated females from becoming pregnant and interrupted pregnancy when given from Day 6 onward. The progesterone level in these females was lowered. A GnRH-antagonist given to ovariectomized females significantly suppressed LH levels, but intact females given artificial vaginal stimulation and treated with an GnRH antagonist became pseudopregnant. These findings indicate that, in the pouched mouse, as in many other rodent species, pseudopregnancy and progesterone production are dependent on prolactin and not on LH.

Plasma levels of gastrin, somatostatin, VIP, insulin and oxytocin during the menstrual cycle in women (with and without oral contraceptives).

The aim of the present study was to investigate whether plasma levels of gastrin, somatostatin, insulin, oxytocin, VIP and blood glucose levels vary during the menstrual cycle. Therefore, 19 healthy menstruating women (5 of whom were on low-dose oral contraceptives, o.c.) were blood sampled every second to third day during the menstrual cycle. Hormone levels were measured with radio-immunoassay. Gastrin, insulin, VIP and blood sugar levels remained unchanged during the menstrual cycle. Mean somatostatin levels were significantly lower in women receiving o.c. than in women without such medication (p less than 0.05). In women on o.c., somatostatin concentrations were also significantly lower during the menstrual week, than during the rest of the period (p less than 0.01), but in women without o.c., no such change occurred. Mean oxytocin levels were significantly higher in women on o.c. (p less than 0.001) and in these women, oxytocin levels recorded during the menstrual week were significantly lower than during the rest of the period (p less than 0.02). Systolic and diastolic blood pressure values were also significantly higher in women on o.c. (p less than 0.05 and p less than 0.01). In conclusion, these data show that basal plasma concentrations of gastrin, somatostatin, VIP, insulin and glucagon do not vary during the menstrual cycle. However, ingestion of low-dose oral contraceptives causes a significant decrease of somatostatin concentrations and a significant increase in oxytocin levels, suggesting that low doses of estrogens and/or gestagens may influence digestive and metabolic processes.

Influence of age and artificial vaginal stimulation on fertility in female bank voles (Clethrionomys glareolus).

Female bank voles mated when 30-50 days old showed only 20-25% fertility at the first mating, but fertility increased to about 80% in animals greater than 100 days of age at the first mating. Young females subjected to artificial cervical stimulation after the completion of a normal mating showed a much higher fertility than normally mated controls (76 compared with 29%). The reason for the low fertility therefore appears to be that young females require more stimulation to activate the corpora lutea than is normally received at a mating.

Neuronal histamine in the gut wall releasable by gastrin and cholecystokinin.

Histamine accumulated in the ligated vagus nerve of the rat, both above and below the ligature; maximum accumulation was after 4 h. The finding is suggestive of axonal flow. Further evidence for histamine in peripheral nerves was obtained in experiments showing that the guinea-pig gut wall could be labelled with [3H]histamine. The experiments were carried out with isolated strips of stomach wall and taenia coli. Electrical stimulation released [3H]histamine from these specimens. The release could be blocked by Ca2+-free medium or by tetrodotoxin. The release was unaffected by vagal denervation or chemical sympathectomy (6-hydroxydopamine) but prevented by reserpinization. Gastrin-17 and cholecystokinin-39 released radioactivity by a tetrodotoxin-sensitive mechanism. The possible existence of a gastrin/cholecystokinin-sensitive neuronal pool of histamine in the gut wall offers a new perspective on the postulated role of histamine as a physiological stimulant of gastric acid secretion and might explain why H2-receptor antagonists block gastrin-stimulated acid secretion.

Activity in the corpora lutea resulting from sterile matings in Clethrionomys glareolus: a histochemical study.

The capacity for steroid production in the corpora lutea (CL) of bank voles was examined by enzyme histochemistry for 3 beta-hydroxysteroid dehydrogenase. The results revealed similar activity in the CL resulting from sterile matings and the CL of pregnancy 2 days after mating. Six days after mating, the CL of pregnancy showed a strong reaction, while there was almost no reaction in the CL from sterile matings, which were clearly regressed at this time. It is suggested that the CL from sterile matings produce progesterone before regression and that this progesterone may prime the luteotrophic complex, increasing fertility of subsequent matings.

Influence of sexual experience and social environment on fertility and incidence of mating in young female bank voles (Clethrionomys glareolus).

Between 30 and 40 days of age, female bank voles were kept singly, in female pairs, separated from an adult male by a wire mesh, or paired with a vasectomized male. At Day 40 they were paired with adult intact males. Fertility at the first mating was low (22-25%), but if the females had previously mated with the vasectomized male fertility of the subsequent mating with the intact male was significantly increased (63%). Sterile matings therefore had a priming effect on the females, and could be important for the development of puberty in wild females. Only 55-59% of the females without contact with males between Days 30 and 40 mated with the fertile male. Contact with a male through a wire mesh increased the proportion to 80% and co-habitation with a vasectomized male to 94%. In the last group, mating also occurred at a younger age.