Blood samples were withdrawn at 10-, 20-or 30-min intervals for 6-12 hr from 13 ovariectomized and 7 intact female rhesus monkeys bearing indwelling cardiac catheters and restrained in primate chairs. Plasma LH and GH concentrations were determined by radioimmunoassay. Twenty-four experiments in ovariectomized animals revealed a striking rhythmic pattern in plasma LH levels having a period of approximately 1 hr, which was asynchronous with variations in plasma GH concentrations when these occurred. The LH oscillations, which had an excursion of 40-92 % of the mean hormone concentration, occurred with a mean period of 75 min and a mode of 60 min. In a typical rhythmic sequence, LH levels increased from nadir to peak during one 10-min sampling interval and decayed exponentially for the next 60 min. The t } calculated from 19 such decay curves based on 10-min sampling intervals was 72 min, which is similar to the estimated tj of exogenous LH in intact females. Moreover, there was a significant positive correlation between the duration of the decay and the magnitude of the next peak. Such oscillations did not occur in intact females. It is suggested that these circhoral (about an hr) oscillations in plasma LH concentrations, occasioned by ovariectomy, represent pulsatile discharges of LH from the pituitary and probably account for the greater part of the elevated LH plasma levels seen in ovariectomized animals. (Endocrinology 87: 850, 1970) I N THE course of experiments performed in bilaterally ovariectomized rhesus monkeys, sampled at relatively frequent intervals, circulating levels of LH were observed to be markedly unstable (1). On detailed examination, sharp oscillations in plasma LH concentrations with a periodicity of approximately one hour were revealed. The following report describes this unexpected phenomenon. Materials and MethodsThirteen adult female rhesus monkeys (Macaco mulatto), weighing 4.6-6.2 kg, were bilaterally ovariectomized under pentobarbital anesthesia and utilized 2 weeks to 7 months after ovariectomy. Seven intact females in the same weight range were also studied.

No abstract

The pulsatile, circhoral discharges of LH observed in ovariectomized rhesus monkeys were blocked within min following single intravenous injections of 17P-estradiol or the initiation of estradiol infusions which achieved physiologic plasma levels of the steroid. The resulting depression in plasma LH concentrations was maintained for several hr after circulating estrogen levels had declined to undetectable values. Pulsatile LH discharges resumed abruptly following this period of inhibition but with a lower frequency and larger magnitude. In contrast, intravenous injections of progesterone had no effect on LH secretion unless massive doses were given, with resultant plasma concentrations of the steroid a thousand fold greater than luteal phase levels. These but caused irregularities in the circhoral rhythm. Similarly, the daily subcutaneous administration of progesterone, in oil, for 2 weeks failed to reduce the elevated plasma LH concentrations in ovariectomized animals. It is concluded that estrogen is the principal participant in the negative feed-back control of tonic LH secretion in primates and that progesterone alone is physiologically inert in this regard. {Endocrinology 90: 771, 1972) W HILE THE NEGATIVE feed-back relationship between the production of the gonadal steroids and the pituitary gonadotropic hormones has been firmly established for some decades, the dynamics of this system as well as the specificity of the interrelationships involved have remained obscure. The advent of radioimmunoassays for the gonadotropins and for the gonadal hormones as well as related techniques for the measurement of circulating steroids has permitted new approaches to this problem. In the rhesus monkey, we have recently shown that gonadectomy results in significant elevations in plasma LH concentrations, within 2 days after the operation. LH levels continue to rise until they reach a plateau,

No abstract

Body weights, organ weights, and blood and pituitary ACTH concentrations were determined in rats exposed continuously to 20.9, 15.0, or 10.0% O2 atmospheres at normal barometric pressure for periods ranging from 3 to 120 hr. Hypoxia resulted in some loss of body weight, and loss of weight of the thymus and the ovary. The weight of the adrenals increased. Blood ACTH rose rapidly after exposure to hypoxic conditions, remaining elevated for the duration of the experiment. Control animals (20.9% O2) placed in the same chamber had detectable blood ACTH only at the 3-hr sampling time. Pituitary ACTH also rose rapidly during hypoxia, the elevation being greatest with the most severe hypoxic state. The rate of ACTH synthesis and secretion in the resting state and during the stress of hypoxia is discussed.