In this paper the problem of the hypothalamic centres involved in the control of gonadotrophin secretion will be presented, based on investigations performed on rats and sheep. The data obtained for the rat were chosen because the control of gonadotrophin secretion in this animal is best known, and therefore this animal may be considered as a model to be compared with the others. On the other hand, the sheep, retaining seasonality of reproductive processes, represents the most natural model of reproduction among farm animals.
E. Domanski, F. Przekop and Jolanta Polkowska
Jolanta Polkowska, Ewa Wolińska and E. Domanski
The relative proportions of prolactin cells, somatotrophs and gonadotrophs were determined in the adenohypophyses of 28 Merino ewes on selected days during the oestrous cycle. Plasma prolactin levels were measured in 16 of the animals at 3-hr intervals during the 24 hr before autopsy. From Days 1 to 5 of the cycle (Day 0=day of ovulation), plasma prolactin levels were 20-40 ng/ml and the prolactin cells were filled with granules. Plasma levels increased to 168 ng/ml between Days 6 and 9, and marked degranulation of the prolactin cells occurred. The greatest degranulation was found on Days 16 and 0, and was associated with a prolactin surge to a concentration of 610 ng/ml. The rise in plasma prolactin and intensive degranulation of prolactin cells at the time of ovulation and formation of the CL suggest that prolactin is important at this stage of the oestrous cycle.
E. DOMAŃSKI, L. SKRZECZKOWSKI, E. STUPNICKA, R. FITKO and W. DOBROWOLSKI
The effect of gonadotrophins on the secretion rate of gonadal hormones in sheep was investigated by perfusing the ovary in situ with luteinizing hormone (lh), luteotrophic hormone (lth) and follicle stimulating hormone (fsh). The gonadotrophins were infused through the side branch of the ovarian artery and the effluent blood was collected from the utero-ovarian vein. Perfusion of the ovary on the 8th day of the oestrous cycle with lh or lth resulted in the increase of the secretion rate of progesterone within 20 to 30 min after the beginning of the perfusion; when the perfusion of the ovary was terminated the rate of progesterone secretion reverted to the original level within 20 to 30 min. Unlike lh and lth, fsh infused on the 8th day of the oestrous cycle decreased the output of progesterone. On the 15th day of oestrous cycle progesterone could not be detected in the effluent blood from the ovarian vein. At that time, perfusion of the ovaries with gonadotrophic hormones produced no effect on the secretion rate of progesterone.
Substances giving positive reaction with Barton's reagent and showing chromatographic characteristics of oestrone and oestradiol were detected in the ovarian venous blood in few animals only, and in very low concentrations. No relation was observed between the presence of these substances in the ovarian venous blood and either the phase of oestrous cycle or the type of gonadotrophin infused. Furthermore, perfusion of the ovary with fsh or lh resulted in the appearance in the ovarian venous blood of an unknown oestrogen-like substance of higher polarity than that of oestrone but lower than that of oestradiol.
E. Domański, F. Przekop, B. Skubiszewski, Barbara Wróblewska and Elżbieta Stupnicka
Domański & Kochman (1968) showed that sheep were more responsive to infusion of purified hypothalamic extract into the adenohypophysis in late anoestrus than in mid-anoestrus. Natural (Schally, Redding, Matsuo & Arimura, 1972) and synthetic (Matsuo, Arimura, Nair & Schally, 1971) LH-RH have been used to induce ovulation in many species, including sheep (Reeves et al., 1972). Administration of a single intravenous injection of 150 μg synthetic LH-RH to seasonally anoestrous ewes induces LH release in all injected animals, but the LH peak is much smaller than that observed at oestrus and luteal function, assessed by peripheral progesterone levels, is absent in most animals (Crighton, Foster, Haresign & Scott, 1975). When the LH-RH was given as five injections the LH peak resembled that at natural ovulation but plasma progesterone levels were still low. Shareha, Ward & Birchall (1976) gave much smaller doses of LH-RH (25 μg/day in continuous infusions for 2 days) to anoestrous ewes but the results were again unsatisfactory.
W. DOBROWOLSKI, EL[unk]BIETA STUPNICKA and E. DOMAŃSKI
Progesterone levels were determined in ovarian venous blood of nine cows with regular oestrous cycles and in three cows with prolonged maintenance of the corpus luteum. The ovarian venous blood was collected by chronic cannulation of the ovarian vein, through the anterior uterine vein. The progesterone level increased from 5·6 μg/100 ml plasma on the 1st day of the oestrous cycle to about 125 μg/100 ml on the 8th day and to about 180 μg/100 ml on Days 14 and 15 of the cycle. Thereafter, the level rapidly decreased to 10 to 20 μg/100 ml on the day of ovulation. In cows with prolonged maintenance of the corpus luteum when ovulation did not occur, the progesterone levels did not decrease and were as high as the highest luteal phase levels in cows with regular cycles. According to the data obtained, progesterone levels in ovarian blood of non-pregnant cows seem to reflect the luteal function of the ovary during the oestrous cycle.