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

The physiological relevance of oestradiol (E(2)) on post-orchiectomy (OX) food intake control was evaluated in six adult, male, domestic, short-hair cats. Jugular venous plasma E(2) and oestrone (E(1)) concentrations were determined weekly before OX and immediately after OX in a cross-over trial of two 3-week periods in which E(2) (0.5 mu g) or vehicle (0.1 ml/kg) was subcutaneously injected daily and blood was sampled 4 h later. Plasma E(1) and E(2) concentrations before OX were 32 (SE 8.3) and 4.3 (SE 1.0) pg/ml, respectively. Following OX, plasma concentrations of E(2) were decreased (P=0.04) while those of E(1) were unchanged. Injections of E(2) increased (P=0.02) plasma E(2) towards pre-OX concentrations. In a second cross-over trial, plasma E(1) and E(2) 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 E(1) and E(2) concentrations. Hence, circulating E(2) appears to be reduced by OX, while it is not significantly changed by body-fat gain. The amount of E(2) injected after OX was not supraphysiological; it restored plasma E(2) to pre-OX concentrations and reduced food intake in five of the six cats by a mean of 14 (SE 3) %.