No abstract

The control of secretion of prolactin was studied using continuous perfusion of a column of isolated rat pituitary cells supported by Bio-Gel polyacrylamide beads. Prolactin secretion was inhibited repeatedly by dopamine and rapidly recovered in its absence. Maximum inhibition was achieved at 5 x 10(-7) M dopamine. Bromocriptine and lergotrile directly inhibited prolactin release from the pituitary cells. Bromocriptine had a longterm action in inhibiting secretion. The dopamine receptor blocking agent, metoclopramide, overcame the inhibitory effect of dopamine but had no effect on prolactin secretion in its absence.

No abstract

Half-hourly blood samples were taken from six clinically euthyroid men over a continuous period of 24 h. Their concentrations of total thyroxine (T4), total triiodothyronine (T3), thyrotrophin (TSH) and prolactin (PRL) were assessed together with the degree of unsaturation of thyroid hormone binding proteins as determined by the thyroid hormone uptake test (THUT). Both T3 and T4 were also measured in urine samples collected serially during the same 24 h period. Significant circadian changes in serum TSH, THUT, serum and urine T4 and serum PRL were demonstrated in all subjects. TSH showed a reciprocal pattern to serum T4, with higher levels during the evening and at night than the daytime. This TSH pattern did not coincide with PRL secretion. Further studies on the same subjects did not show any significant effect of posture, corticosteroid or T4 administration upon circadian changes in TSH. There appeared to be no consistent circadian changes in serum or urinary T3. It seems likely that the TSH circadian rhythm is centrally determined and that free T3 levels are maintained more or less constant by variation in peripheral conversion from T4.

Human pancreatic growth hormone releasing factor (hpGHRF(1-40)) stimulates the release of growth hormone in normal subjects and some patients with growth hormone deficiency. A study comparing the shorter chain amidated analogue hpGHRF(1-29) with an equivalent dose of hpGHRF(1-40) in seven normal subjects showed no significant difference In growth hormone response between the two preparations. Six