Half-life of FSH and LH in the ferret

Anoestrous and oestrous ferrets were injected with luteinizing hormone-releasing hormone (LRH) or a long-acting analogue and subsequently hypophysectomized. Spayed ferrets were hypophysectomized without prior treatment with gonadotrophin releasing factor, and serial blood samples collected from all animals in order to follow the rate of decline in plasma gonadotrophin concentration. The half-life of LH in the spayed female (around 2 h) was much longer than that of the hormone released from the hypophysis of anoestrous females by LRH (25 min) or by the analogue (19 min). The half-life of FSH released by LRH or analogue in anoestrous females was approximately 65 min, while that discharged by the analogue in oestrous females was about 4 h. The fall in plasma FSH concentration in spayed females after hypophysectomy was too slow to allow calculation of a half-life.