The luteinizing hormone response to luteinizing hormone-releasing hormone, prostaglandin E₂ and naloxone is modulated by divergent sensitivity to testosterone feedback

Testosterone (T) levels necessary to suppress LH secretion are reduced in starvation, and increased feedback sensitivity to T is therefore postulated. The luteinizing hormone (LH) response to naloxone (Nal) is more easily suppressed by starvation than is its response to prostaglandin E₂ (PGE₂) and to luteinizing hormone-releasing hormone (LRH). If the divergent suppressibility is due to altered feedback sensitivity in starvation, it should be feasible to reproduce this phenomennon in normally nourished rats by increasing T levels. Adult male Wistar rats were castrated and implanted with silicone capsules (0-2.6 cm) filled with T. Indwelling jugular cannulae were implanted. On days 4 to 8 postoperation rats were injected iv with LRH (25-400 ng/kg body weight), PGE₂ (0.5-1.0 mg/kg body weight) or Nal (0.5-50 mg/kg body weight). Blood samples were drawn before and 10, 20 and 30 min after injection. Results show that the response to Nal was already suppressed at medium T levels. The LH response to PGE₂ was diminished to a greater extent than the response to LRH but was never completely suppressed by increasing steroid levels. These data are compatible with the hypothesis that steroid feedback sensitivity augments with increasing levels of regulation of the hypothalamic-pituitary gonadal axis.