Annual variations in plasma levels of testosterone and luteininzing hormone in the laboratory male mongrel dog.

Blood samples, drawn every 15 days (September 1975-September 1976) from four laboratory-housed male mongrel dogs, were assayed by radioimmunoassay for levels of testosterone and LH in the plasma. The mean plasma concentrations of testosterone remained relatively constant for most of the year with the exception of a significant rise in late August and early September. Mean plasma levels of LH showed a cyclic pattern throughout the year which could be represented by a cosine function curve. However, this cyclic pattern of LH was not accompanied by cyclic changes in plasma levels of testosterone and there was no relationship between these two hormones during the period of 1 year. As the cyclic pattern of LH was altered, the plasma level of testosterone began to rise and reached its highest concentration. Since this alteration of the LH cycle occurred before the increased concentrations of testosterone, and since there was no relationship between these two hormones for the period of a year, we have concluded that there may be another hormone(s) involved which either alters the sensitivity of the canine testis to LH or alters the Lh synthesis/release mechanism of the pituitary gland.

Maintenance of physiologic concentrations of plasma testosterone in the castrated male dog, using testosterone-filled polydimethylsiloxane capsules.

Effects of various numbers of polydimethylsiloxane (PDS) capsules filled with testosterone (PDS-T) on plasma testosterone (PT) in castrated male dogs were studied. Dogs were implanted with 1 empty PDS capsule or 1, 3, or 5 PDS-T capsules. Blood samples were collected prior to and after implantation, after castration with capsules in situ, and after capsule removal. The PT was determined in these samples by radioimmunoassay. One empty capsule had no effect on PT concentration; after castration, PT values fell to nondetectable amounts. One PDS-T capsule maintained PT at concentrations above nondetectable amounts after castration, but these concentrations were significantly (P less than 0.05) lower than were preimplantation values. Three or five PDS-T capsules were capable of maintaining PT concentrations in the castrated male dog similar to those concentrations seen in the intact dog.