Relationship Between Hypothalamic and Median Eminence Catecholamines and Thyroid Function

A central dopaminergic mechanism has been postulated in the control of anterior pituitary (AP) secretion. In the present study, dopamine (DA), norepinephrine (NE), and homovanillic acid (HVA) were determined chemically in the hypothalamus and median eminence (ME) of control and thyroxine-treated rats in order to determine whether a central catecholamine mechanism may be involved in thyroid regulation. Tissue components pooled from groups of 31–45 animals were the ME, the anterior and middle hypothalamus (AMH), and the posterior hypothalamus (PH). HVA was not measurable in any tissue component from either control or thyroxine-treated animals. As expected, a high concentration of DA was found in the ME. However, it was confirmed that NE concentration is significantly higher in the ME than that of DA. Lower concentrations of both NE and DA were found in the AMH and the PH. In the thyroxine-treated animals, PBI was elevated over that of control animals. Following thyroxine treatment, a significant lowering of DA was found in the AMH with no significant difference in NE. No alterations in catecholamine concentration were found in either the ME or PH. These findings indicate that NE is present in higher concentration in the ME than is DA, suggesting that this catecholamine may also be important in AP regulation; suggest that there may be a hypothalamic DA mechanism involved in the regulation of TSH secretion.