SUMMARY

Orchidectomy of Balb C mice aged between 4 and 6 weeks delayed the normal rate of thymic involution. Testosterone replacement after orchidectomy prevented this relative thymic enlargement and testosterone supplements given to intact mice accelerated the normal rate of thymic involution.

When hypopituitary, dwarf mice were given somatotrophin and thyroxine alone there was no significant difference in the thymic weights of control or orchidectomized mice. When replacement therapy included gonadotrophin, orchidectomy was associated with significant thymic hypertrophy. Passive transfer of serum from previously orchidectomized mice did not change the thymic weight of normal recipient mice.

These experiments suggest that testosterone exerts a constant moderating effect on the thymus and the immunological effects of orchidectomy are due to the direct effects of androgen withdrawal.

ABSTRACT

The effects were analysed of a unilateral implant of atropine on ovulation in intact and hemiovariectomized adult rats, together with the response of the atropine-implanted rats to hormone replacement. An outer cannula directed to the left or right preoptic (POA)-anterior-hypothalamic area (AHA) was implanted into cyclic adult rats. A group of animals in oestrus was hemiovariectomized and some were also implanted with a cannula. After two consecutive 4-day cycles, the hemiovariectomized animals were implanted with atropine (23 ± 4 μg) or cholesterol (25 ± 2 μg) on the day of oestrus. Atropine implanted into the left side of the POA-AHA blocked ovulation and compensatory ovarian hypertrophy, whilst implants in the right side had no effects. Administration of gonadotrophin-releasing hormone (GnRH; 3·7 μg/kg) at 13.00 h on the expected day of pro-oestrus induced ovulation in six out of seven treated animals. Of 19 rats with an implant of atropine in the left side of the POA-AHA, one ovulated after treatment with pregnant mare serum gonadotrophin (PMSG) on oestrus, or oestradiol benzoate or human chorionic gonadotrophin (hCG) on day 2 of dioestrus. The effects on ovulation of a unilateral implant of atropine into the POA-AHA of cyclic adult rats and the responses of such rats to GnRH, PMSG, hCG and oestradiol benzoate replacement were also studied. Ovulation was induced in rats with a unilateral implant of atropine and which had been treated with GnRH or hCG at 13.00 h on the expected day of pro-oestrus after the implant. In rats with an atropine implant, treatment with PMSG on the day of implantation or with oestradiol benzoate on day 2 of dioestrus restored ovulation in those with the implant in the left side of the hypothalamus, but was ineffective in those with the implant in the right side. The results suggested that in the adult rat the muscarinic mechanisms regulating preovulatory GnRH release, as well as the stimulatory effects of oestrogen, are lateralized. As the results observed in intact and hemiovariectomized animals subjected to the same treatments were different, it was concluded that the cholinergic neuroendocrine mechanisms regulating ovulation are related to the neural information arising from the ovaries and reaching the POA-AHA.

Journal of Endocrinology (1992) 133, 205–210