Effect of thyrotropin (TSH)-releasing factor (TRF) on plasma TSH levels in nutria (Myocastor coypus)

Intrapituitary or intracarotid infusion of porcine thyrotropin-releasing factor (TRF) into coypu (nutria) failed to increase plasma thyrotropin (TSH) levels. Intravenous administration of TRF into thyroidectomized nutria resulted in an increase in plasma TSH, but the responses were inconsistent. The increase in plasma TSH after TRF was readily demonstrable when thyroidectomized nutria were pretreated with small doses of triiodothyronine. Low sensitivity of the nutria to exogenous TRF may be ascribed, in part, to the relatively low TSH levels in the anterior pituitary gland. These studies nevertheless indicate that TRF can increase plasma TSH levels in the nutria and extend to one more species the evidence of responsiveness to TRF.