Plasma oestrogen changes in adult male cats after orchiectomy, body-weight gain and low-dosage oestradiol administration.

The physiological relevance of oestradiol (E2) on post-orchiectomy (OX) food intake control was evaluated in six adult, male, domestic, short-hair cats. Jugular venous plasma E2 and oestrone (E1) concentrations were determined weekly before OX and immediately after OX in a cross-over trial of two 3-week periods in which E2 (0.5 μg) or vehicle (0.1 ml/kg) was subcutaneously injected daily and blood was sampled 4 h later. Plasma E1 and E2 concentrations before OX were 32 (SE 8.3) and 4.3 (SE 1.0) pg/ml, respectively. Following OX, plasma concentrations of E2 were decreased (P = 0.04) while those of E1 were unchanged. Injections of E2 increased (P = 0.02) plasma E2 towards pre-OX concentrations. In a second cross-over trial, plasma E1 and E2 were determined weekly during the last 3 weeks of two 8-week periods in which food was continuously presented or restricted to 110 % of pre-OX amounts. Continuous food presentation compared with restricted food presentation resulted in greater body weight (6.4 (SE 0.4) v. 5.4 (SE 0.4) kg, P = 0.02) and body fat percentage (29 (SE 3) v. 23 (SE 2) %, P = 0.09) but no significant changes were observed in plasma E1 and E2 concentrations. Hence, circulating E2 appears to be reduced by OX, while it is not significantly changed by body-fat gain. The amount of E2 injected after OX was not supraphysiological; it restored plasma E2 to pre-OX concentrations and reduced food intake in five of the six cats by a mean of 14 (SE 3) %.