[Function of the posterior lobe of the hypophysis in rats under long-term thyroliberin administration]

Thyroliberin injected intraperitoneally to rats in doses of 0.5 microgram/100 g body weight two times a day markedly increased the blood plasma thyrostimulating hormone (TSH) content by the 6th day of using, followed by its decrease down to the control level by the 9th day of the experiment. The blood plasma thyroid hormone levels of these rats were lower than those of the controls by the 6th and 9th days of the test. Photometry of the concentration of the Gomori-positive neurosecretory matter in the posterior hypophysis has shown a significant rise of its amount by the 9th day of the trial. However, changes in the neurosecretory matter did not correlate with the alteration of the TSH- and thyroid hormone levels. Simultaneous administration of thyroliberin and diiodothyrozine (7.5 micrograms/animal) led to the inhibition of thyroliberin TSH-stimulating effect. The above increase in the neurosecretory matter concentration testifies indirectly that long-term thyroliberin injection produces less intensive hormone secretion from the posterior hypophysis into the blood cannel.