The possible existence of peripheral asymmetry in the neuroendocrine mechanisms participating in the response of the ovary to gonadotrophins, and the participation of the vagus nerve, was investigated. At oestrus, the ovulation rate (number of ovulating/number of treated rats) of the left ovary in right unilaterally ovariectomized rats was lower than that in the right ovary in left unilaterally ovariectomized rats (42 vs 84%). No differences in the number of ova shed per ovulating animal nor in compensatory ovarian hypertrophy (COH) were observed. Bilateral section of the vagus nerve resulted in reduced COH only in those animals with the left ovary in situ (right unilaterally ovariectomized). Section of the left vagus nerve induced different effects depending upon which ovary was left in situ. When the left ovary was in situ an increase in ovulation rate, COH and number of ova shed was observed; however, when the right ovary was left in place the above three parameters decreased. Section of the right vagus nerve produced a decrease only in COH in both right and left unilaterally ovariectomized animals. It is concluded that in the unilaterally ovariectomized rat the right ovary seems more able to react to compensatory regulatory systems than does the left. The character of the information carried by the left and right vagus nerve is different.

The modulating effects of ovarian innervation reaching the ovary through the suspensory ovarian nerve on the reactivity of the ovaries to gonadotrophins were analysed. Juvenile rats (32 days old), with or without unilateral or bilateral section of the superior ovarian nerve, were injected with 8 iu of pregnant mare serum gonadotrophin (PMSG), 10 iu of human chorionic gonadotrophin (hCG) or with 8 iu of PMSG followed 56 h later with 10 iu of hCG. Treatments were given immediately after surgery or 4 days later, and the rats were killed on the day of first vaginal oestrus. In rats with unilateral section, treatment with PMSG did not induce full ovulatory response by the denervated ovary whether the treatment was applied immediately or 4 days after surgery (0/11 rats treated immediately ovulated vs 5/5 (sham) and 11/12 (control, P<0·05 Fisher's exact probability test), and 4/19 did when treatment was done 4 days after surgery vs 8/10 (sham) and 11/12 (control, P<0·05). The rats with bilateral section receiving the same hormonal treatment, PMSG administration, ovulated. The number of ova shed by the left ovary was similar to those of the control, while the right ovary released fewer ova. Stimulation with hCG immediately after unilateral section did not induce ovulation in normal or denervated ovary. When the treatment was applied 4 days after surgery, ovulation was observed only in the innervated ovary. In the rats with bilateral section, hCG injection induced ovulation in both ovaries. In those rats with unilateral section of the superior ovarian nerve, the treatment with PMSG+hCG given immediately after surgery resulted in a compensatory ovulation by the innervated ovary (the number of ova shed/ovulating animal was significantly higher than those released by control or sham-operated animals: left section, number of ova shed by the right ovary 7·6 0·3 vs 5·5 0·8 and 4·9 1 respectively, P<0·05; right section, number of ova shed by the left ovary 10·2 0·6 vs 4·4 1·1 and 7·0 0·9, P<0·05), while the denervated one showed a lower ovulation rate as well as a smaller number of ova shed than those by the control animals. When the hormonal replacement was given 4 days after surgery, such compensatory ovulation was observed in the left ovary of those rats with a section of the right nerve (14·3 2·6 vs 4·4 1·1 and 6·5 1·1, P<0·05). When the PMSG+hCG treatment was applied to animals with bilateral section of the superior ovarian nerve, the ovulation rate by the right ovary was significantly lower than in control and sham-operated treated animals (2/10 vs 11/11 and 6/7, P<0·05). Because the ovaries receive innervation through the superior ovarian nerve, the ovarian plexus and the vagus nerve, the results obtained in unilateral denervated animals suggest that the innervation of the ovary via the superior ovarian nerve regulates in a stimulatory way the effects of gonadotrophin resulting in ovulation. The ovulation induced by hormonal treatment of rats with bilateral section of the superior ovarian nerve suggests that the ...

The effects were analysed of secretion of the superior ovarian nerve on compensatory ovulation and ovarian hypertrophy, in adult rats with the left or right ovaries extirpated during the oestrous cycle and autopsied 6 or 20 days later. Rats with hemiovariectomy or hemiovariectomy plus denervation recovered their oestrous cyclicity between 2 and 3 days after surgery. Six days after hemiovariectomy 14 out of 17 rats ovulated on the expected day of oestrus. All the animals were hemiovariectomized on the day of pro-oestrus. The mean +/- S.E.M. number of ova shed was similar to the group of animals with both ovaries (7.8 +/- 1.2 vs 9.5 +/- 0.2). Compensatory ovarian hypertrophy was observed in the right ovary when left hemiovariectomy was performed on day 2 of dioestrus or pro-oestrus; similar results were observed in the left ovary when the right one was extirpated at oestrus or pro-oestrus. Section of the right superior ovarian nerve in left-hemiovariectomized rats caused a reduction in ovulation rate and number of ova released. Compensatory ovarian hypertrophy was modified in the opposite way by unilateral section of the superior ovarian nerve to the in situ ovary depending on the day of the cycle when hemiovariectomy was performed. Twenty days after treatment, ovulation rate, compensatory ovulation and ovarian hypertrophy were similar in both left- or right-hemiovariectomized rats. Compensatory ovarian hypertrophy increased in all animals with section of the superior ovarian nerve, except when hemiovariectomy was carried out at oestrus or the left ovary was extirpated on day 1 of dioestrus.(ABSTRACT TRUNCATED AT 250 WORDS)

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The effects of unilateral section of the right or left vagus nerve (SRVN, SLVN) performed on different days of the oestrous cycle of the rat were analysed. Vagal nerve section on the day of oestrus or on day 1 of dioestrus (D1) altered oestrous cyclicity in a more significant way than when it was performed on day 2 of dioestrus (D2) or pro-oestrus (6/58 maintained normal oestrous cycles compared with 32/39 that did not; P less than 0.01). Ovulation rate at oestrus was lower in rats with SLVN than in the sham-operated group (32/47 vs 28/32; P less than 0.05). The number of ova shed by the left ovary was reduced in sham-operated rats and in animals with SRVN and SLVN, whereas the number shed by the right ovary was not modified. The day of the oestrous cycle on which the vagus nerve was cut also influenced the number of ova shed. No changes in plasma levels of FSH at oestrus were observed in animals with SRVN or SLVN. The results indicate that vagal manipulations performed at the beginning of the oestrous cycle (day of oestrus and D1) induce more changes on oestrous cyclicity and ovulation than when they are performed during the second half of the cycle (D2 and pro-oestrus). In addition, the left ovary is more sensitive to neural manipulation than is the right one.