QUANTITATIVE RELATIONS IN THE AQUEOUS FLARE RESPONSE INDUCED BY ALPHA-MELANOCYTE STIMULATING HORMONE IN THE RABBIT EYES

The aqueous flare response (AFR) to MSH is induced in an increasing percentage of animals with increasing age. The great variability of the responses and the fact that local administration of MSH is not more efficient with lower doses than by subcutaneous injection indicate that the AFR is a complex result in which general factors play a part. The analysis of the variation of the responses has led to a procedure for testing the effect of different preparations.

CUSHING'S SYNDROME FOLLOWING PARTIAL ADRENALECTOMY AND COMPLETE HYPOPHYSECTOMY

A third episode of Cushing's syndrome developed in an adult male who had undergone subtotal adrenalectomy and then complete hypophysectomy in temporarily successful treatment of two earlier episodes. Judging from necropsy findings, this final recurrence was not the result of incomplete pituitary ablation or regeneration of pituitary remnants. Extrasellar pituitary or other ACTH secreting tissue could not be identified, but the patient's marked melanosis suggested its presence with consequent excesses of ACTH or MSH. However, irrespective of whether such excesses did or did not exist, it is clear that the third episode of Cushing's syndrome resulted from hyperfunction of the small adrenal remnant.

GENERAL EFFECTS OF α-MELANOCYTE STIMULATING HORMONE IN THE RABBIT

In addition to the previously described permeability disturbance in the blood aqueous barrier of the eye, measured as an increase of the aqueous flare, a series of transitory systemic effects have been recorded following the subcutaneous injection of synthetic α-MSH:

There is a correlation between the magnitude of the aqueous flare increase and the increase of free fatty acids in plasma and also between the aqueous flare and the minimum serum calcium level.

A melanocyte-stimulating hormone-releasing factor in hypothalamic extracts

Intravenous injection of rat stalk median eminence (SME) extracts to rats produced a decrease in the pituitary melanocyte-stimulating hormone (MSH) activity. This effect was not obtained with injection of cerebral cortex extract, nor with histamine, norepinephrine, vasopressin, or oxytocin. A slight decrease occurred with epinephrine. The response to 2, 1, 1/2, 1/4, and 1/8 of SME was linearly related to the logarithm of the doses. It is inferred that hypothalamic extracts evoked a decrease in MSH pituitary content, since doses of 1/4 SME, which lowered the pituitary MSH activity more than 50%, did not modify the concentration in ACTH. No changes in MSH pituitary activity were obtained in animals submitted to stress. It is concluded that SME extracts contain a MSH-releasing factor which acts directly on the hypophysis and not through the nervous system, since it is effective in rats with hypothalamic lesions in the median eminence area.