Association between leptin receptors in the testicle, leptin and testosterone levels in puber male calves

Objectives. To describe the presence of leptin receptors (ObR) in the testicle during puberty in calves and study the possible association between the expression of the testicles and the levels of leptin (L) and testosterone. Materials and methods. During 7 months every two weeks on six Holstein x Zebu calves, concentrations of testosterone and L were measured by RIA. They were castrated unilaterally according to their peribubertal periods in order to study by RT-PCR the expression of the L receptor isoforms. The statistical analysis was done with the Statistica® program. Results. The levels of testosterone were <1ng/mL at 6 and 6.5 months of age, concentrations of 5.3 ng/ml at 12.5 months were reached before puberty, moment in which the animals had levels of 4.01±1.8 ng/ml. The L concentrations varied between 0.61 and 0.98 ng/ml, with a concentration at puberty of 0.91±0.05 ng/ml. Two isoforms, OBRi and OBRb, were found and correlated significantly at puberty. Negative correlations were found between OBRi-OBRb and the testosterone and L (p=0.08) levels. Testosterone and L levels showed a significant direct correlation. Conclusions. A possible direct effect of leptin on calf gonads until they reach puberty is suggested. The correlation between the OBR isoforms and their association to leptin and testosterone concentrations also suggests the complimentary or joint action of both OBR receptors in peripubertal calves' gonads.