Melanocyte-stimulating Hormone Activity Research Articles

Purification of hypothalamic melanocyte-stimulating hormone (MSH)-releasing factor with Sephadex.

SummaryAcetone powders prepared from ovine stalk-median eminence tissue were extracted with glacial acetic acid and the glacial acetic acid extract was lyophilized. An ammonium acetate extract of the resultant pow-der was filtered through a column of Sepha-dex G-25. The eluent was assayed for its ability to deplete the pituitary of MSH. Extracts were injected i.v. into normal male rats which were sacrificed 20 minutes later. The MSH activity in pituitaries from rats receiving extracts was compared to that found in pituitaries from diluent-injected controls. MSH activity was estimated in an in vitro assay by microscopic grading of the melano-cytes. An active zone was eluted from the column. At the peak of this zone 65-70% of the MSH activity had disappeared from the pituitaries of the test rats. The MSH-releasing zone was separated from the zones which contained CRF, GH-RF, LH-RF, PIF and vasopressin, but overlapped the zone which contained FSH-RF. It was concluded that MSH-RF can be added to the family of...

Melanocyte-stimulating hormone activity of synthetic MSH and ACTH peptides, in vivo and in vitro.

SIMULTANEOUSLY performed in vivo and in vitro determinations of the melanocyte-stimulating hormone (MSH) activity of a large number of synthetic MSH and ACTH peptides have not been reported previously. The work recorded here compares by both methods the MSH activity of 10 stereoisomeric pentapeptide fragments of MSH and 8 synthetic peptides related to ACTH. The MSH activity of most of the stereoisomers appeared greater in vivo than in vitro. When, these compounds were assayed at various time intervals, some of the pentapeptides revealed differences which may help partially to explain this discrepancy in activity between the two methods. These differences may also help in understanding the alterations of α-MSH induced by sodium hydroxide1,2. In addition, preliminary studies were performed on the inhibitory properties of the stereoisomers.

Melanocyte-Stimulating Hormone Activity in Pituitaries of Frogs with Hypothalamic Lesions

Melanocyte-stimulating hormone (MSH) activity in pituitaries of frogs with hypothalamic lesions was compared by bio-assay with the activity of this hormone in pituitaries of intact frogs. There was a significant loss of MSH activity following hypothalamic destruction. The specificity of the assays was substantiated by simultaneous assays of ACTH activity, which was found to be similar in both groups. MSH activity demonstrated by parabiosis was greater in body fluids of lesioned frogs than in the controls. It appeared, therefore, that there was increased pituitary secretion and decreased pituitary storage of MSH activity in frogs with hypothalamic lesions. (Endocrinology 77: 45, 1965.)

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.

MELANOCYTE-STIMULATING HORMONE (MSH) AND ACTH ACTIVITIES OF PITUITARY HOMOGRAFTS IN ALBINO RATS.

The MSH and ACTH activities of renal capsular pituitary homografts in hypophysectomized albino rats were assayed and compared with the activities of these hormones in intact control pituitaries. The ratio of MSH to ACTH in the intact pituitary was approximately 6 times greater than that in the grafted pituitary. This difference was due largely to the loss of MSH activity in the transplants. Since no MSH activity was demonstrated in the plasma of the homografted rats, MSH secretion could not be evaluated. (Endocrinology75: 187,1964)

Melanocyte stimulating hormone activity of different pituitary preparations.

Summary1) Bioassays of various pituitary preparations were made to compare quantitative and qualitative characteristics of the different MSH active principles known to be present in such preparations. Results suggest that the 3 chemically distinct pituitary fractions possessing MSH activity (i.e., alpha-MSH, beta-MSH, and ACTH) act on melanophores in a qualitatively similar manner. It is estimated that the intrinsic MSH activity of ACTH can not be greater than 1/10th that of alpha-MSH. 2) A melanophorotropic activity unit (MAU) is proposed which is defined as the amount of active principle producing 1/2 maximal response (or greater) in 50% of the treated animals. The approximate relationship of MAU to “units” used by other investigators is discussed. The frog bio-assay is sensitive to 0.01 MAU and therefore could be used to measure as little as 10-3 μg of pure ACTH (corresponding to 10-4 I.U. of ACTH) provided this fraction can be completely separated from the other MSH active principles by previous chemi...