OVULATION RATE AND THE CONCENTRATIONS OF LH, FSH, GH, PROLACTIN AND INSULIN IN EWES INFUSED WITH TRYPTOPHAN, TYROSINE OR TYROSINE PLUS PHENYLALANINE DURING THE LUTEAL-PHASE OF THE ESTROUS-CYCLE

Dietary amino acid precursors for cathecholamineric and serotonergic n eurotransmitters may be important in the mechanism of nutritional effe cts on ovulation rate. This paper reports the results of three experim ents that examined the effect of such amino acids on ovulation rate an d the concentrations of FSH and LH in sheep, In three separate experim ents, groups of ewes were infused, over Days 9 to 13 of the oestrous c ycle, with either tryptophan (n = 11), tyrosine (n = 11) or a mixture of tyrosine and phenylalanine (n = 11). Control ewes (n = 12 in each e xperiment) were infused with a vehicle over the same period. None of t he amino acids infused effected ovulation rate or plasma concentration s of LH, FSH, GH or prolactin. The infusion of a mixture of tyrosine a nd phenylalanine increased insulin concentrations. The infusion of the se amino acids was not associated with changes in gonadotrophin concen trations and therefore the effect of nutrition on ovulation rate in ew es does not seem to involve an increase in the availability of tryptop han, tyrosine or phenylalanine. Increasing the uptake of other amino a cids that compete with tryptophan, tyrosine or phenylalanine for the l arge neutral amino acid transporter may cause a decrease in the availa bility of tryptophan, tyrosine or phenylalanine thereby eliciting the effects of nutrition on ovulation rate. However, this hypothesis remai ns to be tested.