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Plasma gonadotrophin and androgen concentrations in a freemartin ewe and its male sibling

Investigations of plasma gonadotrophin concentrations in intact ewes have shown that, in general, LH concentrations are low and fairly stable whereas FSH levels, which are much higher, may fluctuate from 15 ng to over 100 ng FSH/ml (Salamonsen et al., 1973). However, this apparent independence of the tonic levels of plasma LH and FSH is replaced by a close association of surges of both hormones at oestrus or when provoked by oestrogen, LH-RH, or progesterone-implant removal (Reeves et al., 1972; Salamonsen et al., 1973; Jonas et al., 1973; Reeves, Beck & Nett, 1974; Symons, Cunningham & Saba, 1973, 1974; Saba, Cunningham, Symons & Millar, 1975). In marked contrast, plasma gonadotrophin concentrations in the mature ram show episodic fluctuations in plasma LH, which are not correlated with changes in FSH levels (Katongole, Naftolin & Short, 1974; Lee et al., 1976a). This difference between ewes and rams is also evident in the response to LH-RH; the mature ram shows an increase in plasma LH but very little or no increase in plasma FSH concentrations (Hopkinson, Pant & Fitzpatrick, 1974; Lee et al., 1976b).