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Biomedical subjects

M E Hadley

Publications and source records attributed to M E Hadley.

At least 145 records · Page 8Linked to original sources
PubMed1971

Calcium requirement for melanophore-stimulating hormone action on melanophores.

The calcium ion is specifically required for the action of melanophorestimulating hormone on melanosome dispersion within lizard (Anolis carolinensis) melanophores in vitro. The response to this hormone is directly related to the concentration of the Ca(2+) ion. Lithium, choline, rubidium, and cesium will replace the sodium and potassium of Ringer solution if Ca(2+) is present. Calcium ions are not required for melanosome dispersion itself, since theophylline or dibutyryl cyclic adenosine monophosphate reversibly darkens lizard skins in the absence of calcium.

Animals↗
PubMed1970

Evidence for separate receptors for melanophore stimulating hormone and catecholamine regulation of cyclic AMP in the control of melanophore responses.

1. Skins of the lizard Anolis carolinensis darken in vitro in response to melanophore stimulating hormone (MSH), a peptide hormone, as well as to catecholamines. These hormones darken Anolis skins by dispersing the sub-cellular organelle, the melanosome, out into the dendritic processes of the dermal melanophores.2. Dibutyryl cyclic AMP and methylxanthines also darken skins. In addition, methylxanthines are synergistic with both catecholamines and MSH in causing skin darkening. These data suggest that the dispersion of melanosomes within melanophores in response to both MSH and catecholamines is mediated by cyclic AMP.3. alpha-Adrenoceptor blocking agents inhibit MSH-induced darkening but potentiate catecholamine-induced darkening. beta-Adrenoceptor blocking agents, in contrast, inhibit catecholamine-induced darkening but have no effect on MSH-induced darkening. This selective blockade of one receptor while the functional integrity of the other receptor is maintained suggests that MSH and catecholamines increase cyclic AMP levels through different receptors.4. Catecholamines exert their action through beta-adrenoceptors; MSH darkens skins through what appears to be a component of the alpha-adrenoceptor. beta-Adrenoceptor stimulation may stimulate adenyl cyclase to increase cyclic AMP levels whereas MSH may inhibit cyclic AMP phosphodiesterase thereby preventing cyclic AMP breakdown.

Adenine Nucleotides↗
PubMed1969

Effects of cyclic 3',5'-AMP and other adenine nucleotides on the melanophores of the lizard (Anolis carolinensis).

1. Cyclic 3',5'-AMP has been reported to darken skins of the frog, Rana pipiens. This suggests that cyclic 3',5'-AMP may mediate the action of MSH on amphibian chromatophores. Since MSH also darkens skins of the lizard, Anolis carolinensis, we investigated the effects of cyclic 3',5'-AMP and other nucleotides on Anolis melanophores to determine whether cyclic 3',5'-AMP may be the intracellular mediator of hormone action on melanophores of another vertebrate class.2. Cyclic 3',5'-AMP, itself, causes a rapid melanin granule aggregation within melanophores of Anolis. This response is, however, somewhat nonspecific in that both 5'-ATP and 5'-ADP also lighten the skins by aggregating the melanin granules. Another nucleotide, 5'-AMP, darkens the skins by dispersing melanin granules. Cyclic 2',3'-AMP does not darken or lighten Anolis skins.3. Dibutyryl cyclic 3',5'-AMP, which is considered to be better able to penetrate membranes and resist degradation by a specific phosphodiesterase, maximally darkens Anolis skins, as does MSH. This darkening by the potent dibutyryl cyclic 3',5'-AMP suggests that cyclic 3',5'-AMP may be the intracellular mediator of melanin granule dispersion within Anolis melanophores leading to skin darkening.4. Other evidence supporting the first-messenger-second-messenger hypothesis for melanophore regulation is discussed.5. The differences in responses of Anolis melanophores to adenine nucleotides may relate to the ability of these agents to penetrate melanophore membranes; thus, the nucleotides could exert their effects either intracellularly or extracellularly on the plasma membrane.

Adenine Nucleotides↗