Effects of Testosterone and Testosterone Propionate Administration on Luteinizing Hormone Secretion in the Male Mongrel Dog1

Studies were carried out to determine the effect of either multiple or single s.c. injections of oil, testosterone (T) (500 µg/kg) or testosterone propionate (TP) (500 µg/kg) on resulting T and LH concentrations in the plasma of intact and castrated male mongrel dogs. The multiple injections were given once daily for 7 days with daily blood samples collected prior to, during and after injections. In the single injection study, blood samples were collected 1 h before injection, every 20 min for 3 h after injection and every 3 h thereafter for a total of 24 h. In both studies T and LH were determined by RIA. The results of these experiments indicate that T, in contrast to TP, induces a more rapid but shorter-lived increase in plasma T and consequently a more rapid inhibition of LH secretion. These data suggest that sample interval following either T or TP administration is important when testing their effect on the hypothalamic-pituitary axis.