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

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Abstract
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.