Changes in plasma thyrotrophin-releasing hormone, thyrotrophin, prolactin and thyroid hormone levels after intravenous, intranasal or rectal administration of synthetic thyrotrophin-releasing hormone in man.

Changes in plasma thyrotrophin-releasing hormone (TRH), thyrotrophin (TSH), prolactin and thyroid hormone levels after iv, intranasal, or rectal administration of synthetic TRH were studied in man. The plasma TRH concentration increased with all three routes, but remained at higher levels for a longer time after intranasal or rectal administration, in contrast to the rapid decrease after iv administration. Plasma TSH, prolactin and thyroid hormone levels increased significantly after intranasal or rectal administration and also remained elevated for a longer period than iv administration. These findings suggest that TRH administered intranasally or rectally enters the blood stream and stimulates TSH, prolactin and thyroid hormone release in man.