Plasma cortisol response to thyrotrophin releasing hormone and luteinizing hormone releasing hormone in healthy kennel dogs and in dogs with pituitary-dependent hyperadrenocorticism

The change in the plasma concentration of cortisol after the administration of thyrotrophin releasing hormone (TRH) and LH releasing hormone (LH-RH) was studied in normal dogs and in dogs with pituitary-dependent hyperadrenocorticism (PDH). The normal dogs showed a small but significant increase in the plasma concentration of cortisol 15 min after intravenous injection of TRH and LH-RH. In ten of the dogs with PDH the response to TRH was not significantly different from that in the normal dogs, but in 13 the response was significantly greater. In 15 of the dogs with PDH the response to LH-RH administration was within or below the range of responses in the normal dogs and in only one dog was the response to LH-RH greater than that in the normal dogs. These findings are discussed in relation to the pathogenesis of PDH.