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ABSTRACT
Skin tyrosinase activity increases during hair growth in C3H–HeA*vy mice and reaches higher levels in young (30- to 35-day-old) mice when the hair follicular melanocytes synthesize the black pigment, eumelanin, than in older (6-month-old) mice when they produce the golden yellow pigment, phaeomelanin. To examine the regulation of the melanocytes at these different stages we have compared the effect of α-MSH and other agents that act, through cyclic AMP-dependent mechanisms, on skin tyrosinase activity in both young and old mice during hair growth, initiated by plucking. Daily administration of α-MSH, isoprenaline or theophylline increased coat darkness, and skin tyrosinase activity in the younger mice 7–9 days after plucking, but they were ineffective in the older mice. Similarly α-MSH, 8-bromo-cyclic AMP or theophylline increased tyrosinase activity in skin explants from the younger mice incubated for up to 24 h but had no effect in explants from older mice. Cyclic GMP had no effect on tyrosinase activity in skin explants from both young and old mice. It is suggested that whereas cyclic AMP-dependent mechanisms may operate to regulate tyrosinase activity in the hair follicular melanocytes of younger mice that produce eumelanin these systems may not operate in the older mice when these melanocytes synthesize phaeomelanin. Phaeomelanin synthesis, unlike that of eumelanin, may not depend upon tyrosinase and its regulation by cyclic AMP and this could explain the low levels of this enzyme in the skin and its failure to respond to α-MSH and other activators of the cyclic AMP system during periods of phaeomelanin production.
J. Endocr. (1986) 111, 225–232
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ABSTRACT
Bromocriptine, a dopamine agonist that blocks the secretion of MSH, inhibits melanogenesis in the hair follicular melanocytes of pubertal C3H–HeA*vy mice. However, since this effect cannot be explained by a reduction in circulating α-MSH, we have examined the possibility that dopaminergic mechanisms may have a direct inhibitory effect on these melanocytes.
Bromocriptine decreased tyrosinase activity in skin explants from 30- to 35-day-old mice that were growing dark hair. This decrease in tyrosinase activity was blocked by dopamine receptor antagonists, haloperidol or spiperone. The specific D2 agonist LY 171555 also inhibited tyrosinase activity in the skin explants in a dose-related manner and the effect was blocked by sulpiride, a D2-receptor antagonist. Neither bromocriptine nor LY 171555 had any effect on tyrosinase activity in skin explants taken from adult mice that were growing yellow hair. The D1-receptor agonist SKF 38393 had no effect on tyrosinase activity in skin explants from either group of mice.
The present results support the idea that dopamine D2-receptor agonists have a direct inhibitory effect upon tyrosinase activity of hair follicular melanocytes of the C3H–HeA*vy mouse. However, this effect was confined to periods of dark hair growth when the melanocytes produce eumelanin. The D2 agonists were ineffective in reducing tyrosinase activity during adult life when the melanocytes produce predominantly phaeomelanin. This suggests that different control mechanisms may operate in the hair follicular melanocytes during periods of eumelanin and phaeomelanin synthesis.
J. Endocr. (1986) 111, 233–237
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In a recent radioimmunoassay for human β-melanocyte-stimulating hormone (βh-MSH) (Thody & Plummer, 1973) the dextran-coated charcoal technique (Herbert, Lau, Gottlieb & Bleicher, 1965) was used for the separation of antibody-bound and free hormone. We have now examined several other methods of separation.
Details of the antiserum and iodination of synthetic βh-MSH have been described (Thody & Plummer, 1973). Tubes were set up containing 25 pg 125I-labelled βh-MSH and diluted antiserum in 210 μl diluent buffer (0·05 m-phosphate buffer, pH 7·4 containing 0·5% human serum albumin and 0·02% thiomersal (Merthiolate)). The final dilution of antiserum was 1:8250, sufficient to bind approximately 50–70% of 125I-labelled βh-MSH (Thody & Plummer, 1973). Blanks containing no antiserum were set up in parallel. After incubation for 24 h at 4 °C antibody-bound and free 125I-labelled βh-MSH were separated. For separation by the second
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SUMMARY
The adenohypophysis of the pig was examined histochemically for the presence of 11 oxidative enzymes, namely: 1.1.1.27 l-lactate: NAD oxidoreductase, 1.1.1.30 d-3-hydroxybutyrate: NAD oxidoreductase, 1.1.1.37 l-malate: NAD oxidoreductase, 1.1.1.41 threo-d s-isocitrate: NAD oxidoreductase (decarboxylating), 1.1.1.42 threo-d s-isocitrate: NADP oxidoreductase (decarboxylating), 1.1.1.49 d-glucose-6-phosphate: NADP oxidoreductase, 1.1.99.5 l-glycerol-3-phosphate: (acceptor) oxidoreductase, 1.3.99.1 succinate: (acceptor) oxidoreductase, 1.4.1.2 l-glutamate: NAD oxidoreductase (deaminating), 1.6.99.1 reduced-NADP: (acceptor) oxidoreductase, 1.6.99.3 reduced-NAD: (acceptor) oxidoreductase.
With the exception of 1.1.1.30 d-3-hydroxybutyrate: NAD oxidoreductase, activity was found throughout the adenohypophysis for all these enzymes. A comparison was made with the activity for these enzymes in liver.
In the adenohypophysis, the pars tuberalis exhibited the highest activity for all enzymes, generally equal to or greater than that shown by the liver. The pars intermedia and the pars anterior showed similar activity for these enzymes, in general of a lower order than that given by the liver. The pattern of enzyme distribution in the pars intermedia is described; high activity for 1.1.1.37 l-malate: NAD oxidoreductase, 1.1.1.27 l-lactate: NAD oxidoreductase, 1.6.99.3 reduced-NAD: (acceptor) oxidoreductase, 1.6.99.1 reduced-NADP: (acceptor) oxidoreductase was shown by cells lining cysts and the pituitary cleft.
The findings are discussed in relation to the possible association of these enzymes with secretory function.
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SUMMARY
A method is described for the radioimmunoassay of β-melanocyte-stimulating hormone (β-MSH) in human plasma. It was capable of detecting 20–30 pg β-MSH and was unaffected by the presence of α-MSH and human adrenocorticotrophic hormone. However, cross-reactivity did occur with β-glutamyl MSH (porcine).
A simple technique employing porous glass (Florisil) was used to extract β-MSH from plasma. In normal male subjects plasma β-MSH levels ranged from 21 to 133 pg/ml. In patients receiving cortisol therapy for Addison's disease slightly elevated levels were found. Much higher levels were found in patients who had undergone bilateral adrenalectomy as treatment for Cushing's disease.
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SUMMARY
The changes in the content of melanocyte-stimulating hormone (MSH) and histology of the neuro-intermediate (n.i.) lobe were followed in rats which drank 2% sodium chloride for periods from 1–15 days.
The pars intermedia showed a biphasic response. During the initial phase of 1–4 days there was a rapid rise in the MSH content, by 153% in the first day, falling back to control level by 4 days. These fluctuations were paralleled by an increase in the normally small numbers of Type 2 cells and at the same time numerous Type I cells showed hypertrophy and degranulation.
After 4 days on saline there was a second rise in the MSH content, which was still evident at 15 days; during this second period the number of Type 2 cells declined to normal levels. The degranulated Type 1 cells also disappeared, most of Type 1 being smaller in size and intensely PAS-positive.
After the ingestion of saline it apparently takes several days before the pars intermedia adapts to a new level of activity.
The likely significance of these changes and the possibility of a relationship between the pars intermedia and the neurohypophysis are discussed.
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Sexually experienced male rats were used to test for whole body and preputial gland odours of female rats. The male rats clearly preferred whole body odours of intact female rats to those of preputialectomized female rats. The male rats also preferred the odour of preputial gland tissue of intact female rats to that of ovariectomized female rats and were especially attracted to the preputial gland odours of female rats in pro-oestrus and oestrus. The preputial gland odours of ovariectomized rats that had received oestradiol benzoate for 7 days were attractive to male rats, although similar treatment with progesterone was ineffective. However, a single injection of progesterone given 72 h after a single injection of oestradiol benzoate not only made ovariectomized rats receptive, but also made their preputial gland odours attractive to male rats.
The results suggest that the preputial gland of the female rat is responsible for odours that serve to attract sexually experienced male rats. Ovarian steroids, as well as controlling receptivity in the female rat, would also appear to control the production of sex attractants in the preputial gland. There was no relationship between the size of the preputial glands and their ability to attract male rats which suggests that preputial gland growth and production of sex attractants are not under the same hormonal control.
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The anterior pituitary has an important role in the control of sebaceous gland activity. This effect is mediated in part by thyrotrophic hormone (TSH) and adrenocorticotrophic hormone (ACTH) through their actions on the thyroid and adrenal glands respectively (Thody & Shuster, 1970a, 1971, 1972a). Ablation and replacement experiments suggest that the gonads also have a major influence (Thody & Shuster, 1970a, b), but although there is evidence that gonadotrophins will stimulate sebaceous glands in the human male (Strauss & Pochi, 1963) no data are available from experimental animals. We therefore decided to examine the effect of gonadotrophins on sebum secretion in the rat.
Male Wistar rats were hypophysectomized when 8–9 weeks old and 4 weeks later received either 0·9 units human menopausal gonadotrophin (Humegon)/day or no treatment. Humegon was dissolved in 0·9% NaCl solution and subcutaneous injections were given daily for a period of 2 weeks. At
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Removal of the pituitary gland from the rat produces a decrease in the rate of sebum secretion (Nikkari & Valavaara, 1969; Ebling, Ebling & Skinner, 1969; Thody & Shuster, 1970 a). However, it is not established which pituitary hormones are involved in the control of sebaceous gland activity. In this study we have examined the effect of a new pituitary hormone, β-lipotrophin (β-LPH) (Birk, & Li, 1964; Li, 1968), on the rate of sebum secretion in the rat.
Female Wistar rats were ovariectomized when 5–6 weeks old and hypophysectomized at 7–8 weeks of age. Two weeks later the rats were divided into two groups and received either no hormone treatment (controls) or 0·1 mg β-LPH/day. The injections were given subcutaneously and continued for 2 weeks. At the end of this time the rate of sebum secretion was measured by the method of Archibald & Shuster (1970).
In this method the
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Increased circulating levels of melanocyte-stimulating hormone (MSH) have been found in patients who had undergone adrenalectomy for Cushing's disease and in patients with Addison's disease; these increased levels were suppressed by glucocorticoid treatment (Abe, Nicholson, Liddle, Orth & Island, 1969; Thody & Plummer, 1973). In this study we report the absence of an effect on MSH secretion after adrenalectomy and dexamethasone treatment in the rat.
Adult female Wistar rats were divided into three groups, A, B and C. When 10 weeks old, groups B and C were adrenalectomized. These rats then received 1% saline in place of tap water. Two weeks after adrenalectomy group C received daily, subcutaneous injections of 250 μg dexamethasone sodium phosphate (Organon Laboratories Ltd) in 0·9% saline. Groups A and B received saline only. Two weeks later the rats were anaesthetized with sodium pentobarbitone (Nembutal) and decapitated. Neck blood was collected in heparinized polystyrene tubes and
