Effects of alpha-MSH on kainic acid induced changes in core temperature in rats

The effects of intraperitoneal (i.p.) administration of kainic acid (KA) and alpha-melanocyte-stimulating hormone (alpha-MSH) alone or in combination, on core temperature of freely moving rats were examined. KA or saline was administered once (10 mg/kg) and alpha-MSH or saline was given repeatedly i.e. 10 min before and 10, 30 and 60 min after the administration of saline or KA. Two doses of alpha-MSH were used: 0.5 and 2.5 mg/kg. KA alone produced a biphasic effect on core temperature, i.e. an initial short-lasting hypothermia followed by hyperthermia that lasted about 6 h. The higher dose of alpha-MSH had a potentiating effect on KA-induced hypothermia, while the lower dose of alpha-MSH increased the hyperthermia produced by KA. alpha-MSH administered alone produced a late (3 h), dose-dependent increase in core temperature. It is conceivable that repeated administration of alpha-MSH in the doses used in our study may cause a cumulative effect in raising body temperature for a limited period of time.The previously described interactions between KA and alpha-MSH, respectively, with dopaminergic and serotoninergic systems may account for the effects on core temperature in rats observed in our study.     

Interaction of MIF-I or alpha-MSH with D-amphetamine or chlorpromazine on thermoregulation and motor activity of rats maintained at different ambient temperatures

Administration of several doses of MIF-I or alpha-MSH did not modify colonic temperature or the level of motor activity of rats in ambient temperatures of 4 degree or 20 degrees C. However, the thermoregulatory but not motor effects of the interaction between MIF-I or alpha-MSH with d-amphetamine were dependent upon ambient temperature. At 4 degree C, 1.0 mg/kg of both peptides enhanced the d-amphetamine-induced hypothermia, but at 20 degrees C both peptides blocked the hyperthermic effects of d-amphetamine. The hypothermic effect of chlorpromazine (CPZ) at 4 degree C and 20 degrees C was blocked by 1.0 mg/kg MIF-I but not by 1.0 mg/kg alpha-MSH. No linear dose response relationships between various doses of MIF-I or alpha-MSH and thermal responses were found. Administration of melanin or the use of hypophysectomized rats did not alter the significant interactions observed after peripheral injections.     

Effect of alpha-melanotropin hormone on serum levels of luteinizing hormone and progesterone in experimental rat autoimmune oophoritis

We studied the effect of alpha-melanotropin hormone (alpha-MSH) on experimental autoimmune oophoritis (EAO), an inflammatory process induced in female rats. During proestrus, serum levels of LH and progesterone in rats with EAO were higher than those of control rats. However, administration of alpha-MSH to these rats decreased the levels of LH. Similarly, in the following diestrus, rats with EAO had high levels of LH but treatment with alpha-MSH decreased the levels to diestrus 2 control values. Treatment with alpha-MSH also reduced the LH levels of control rats in diestrus 2 compared to untreated controls. However, alpha-MSH treatment had no effect on progesterone levels of either control or rats with EAO. Thus, although alpha-MSH induced notable changes in levels of LH, this decrease was unable to block the illness.     

Refractory hypothalamic alpha-mSH satiety and AGRP feeding systems in rats bearing MCA sarcomas

In pre-anorectic tumor-bearing (TB: methylcholanthrene-induced sarcoma) rats, injection of alpha-melanocyte stimulating hormone (alpha-MSH) into the perifornical hypothalamus (PFH) had no significant effect on food intake at a dose (5 microg) that reduced feeding in non-TB control rats. Following the development of anorexia, injection of alpha-MSH MC3/MC4 receptor antagonists, SHU9119 (1 microg) or 4 microg agouti-related protein (AGRP), stimulated feeding in non-TB rats, while having no significant effect in TB rats. Concentrations of alpha-MSH were not altered significantly in ventromedial, dorsomedial or lateral hypothalamic areas of TB rats, and proopiomelanocortin (POMC) messenger RNA was not changed in TB rats in these hypothalamic areas. Determination of cytokines by ELISA in non-operated TB and non-TB rats revealed elevated IL-2 in plasma and hypothalamus as well as increased TNF-alpha in the hypothalamus of anorectic TB rats. IL-1B was not detectable in plasma and was not altered significantly in hypothalamus of TB rats. These results suggest that the POMC alpha-MSH satiety system is refractory in TB rats, even prior to the onset of anorexia. This change in MC3/MC4 receptor response does not appear to be secondary to alterations of endogenous alpha-MSH in TB rats. Cytokine involvement in the altered response to MC3/MC4 receptor stimulation and blockade is a possibility, since TNF-alpha and IL-2 were increased in hypothalamus of anorectic TB rats. Therefore, these results suggest major alterations in POMC neuropeptide systems in TB rats as anorexia progresses. Although these changes do not appear to have occurred due to grossly-altered concentrations of alpha-MSH, elevated cytokine activity in the hypothalamus may be an important factor. Due to the complex multi-factorial nature of feeding control, additional factors are likely to be involved in cancer anorexia.     

Central alpha-MSH infusion in rats: disparate anorexic vs. metabolic changes with aging

Changes of the anorexigenic and hypermetabolic components of the overall catabolic effect of alpha-MSH were studied in rats as a function of age. In male Wistar rats a 7 day-long intracerebroventricular infusion of alpha-MSH suppressed food intake and caused a fall in body weight in 2 and 3-4 month-old (young) groups, but it was most effective in the 24 month-old group and had hardly any effect in the 12 month-old (middle-aged) animals. In contrast, metabolic rate as well as biotelemetric measurements of core temperature and heart rate revealed the most pronounced hypermetabolic effects of such infusions at age 12 months. The hypermetabolic effect was still high in the oldest group, but low in the younger groups. In conclusion: Changes of the anorexigenic and hypermetabolic effects in the course of aging are not concordant. The overall catabolic activity of alpha-MSH is smallest in the middle-aged and highest in the oldest group.     

The effect of alpha-melanophor-stimulating hormone on liver regeneration and incorporation of amino acid in rats' liver protein.

Following 25 mug/day synthetic alpha-MSH administration, the liver regeneration of partially hepatectomized rats proved to be increased. The hormone treatment resulted in an enhanced alanine incorporation of the liver proteins, but this effect was uncertain on partially hepatectomized rats. Due to the hormone treatment the low liver protein content of the operated rats became normal. The pseudocholinesterase activity of the liver homogenate of alpha-MSH treated rats was also elevated. On the basis of these experiments authors are supposing some protein synthesis increasing effect of synthetic alpha-MSH.     

Functional and biochemical parameters of peptide antigen presentation

To understand the mechanism by which peptide antigens are processed and presented to T cells, we examined the T-cell response to the 13-amino-acid peptide alpha-melanocyte-stimulating hormone (alpha-MSH). To determine the fine specificity of T-cell recognition, T cells specific for alpha-MSH, and genetically restricted by I-Ab/d, were challenged with different alpha-MSH analogs and homologs. It was found that intact alpha-MSH, including the blocked amino and carboxy termini of the native molecule, was required for T-cell responsiveness. Antigen-presenting cells (APC) could be briefly pulsed with alpha-MSH and then present the alpha-MSH antigenic determinant to T cells, indicating that the relevant antigen was retained by the APC. APC stimulatory capacity was dramatically reduced by aldehyde treatment of the APC, or by pulsing the APC with alpha-MSH at low temperature. Efficient alpha-MSH pulsing was also impaired by treatment of the APC with the carboxylic ionophore, monensin, but not by the lysosomotropic agents chloroquine and methylamine. In addition, isolated APC plasma membranes added to the T cells in the presence of soluble alpha-MSH were not stimulatory. However, plasma membranes isolated from APC that had been previously pulsed with alpha-MSH retained stimulatory activity for T-cell responses. The only detectable alpha-MSH contained in these pulsed APC membranes was in an acid-stable complex of higher molecular weight than native peptide. The amount of alpha-MSH detected in the cellular membrane fraction isolated by density gradient sedimentation was also reduced by treatments that reduced the APC stimulatory capacity, such as pulsing at low temperature or in the presence of monensin. Taken together, these results suggest that processing of alpha-MSH is unlike that heretofore described for other peptide antigens and seems to involve APC handling to form the stimulatory moiety presented on the APC surface.     

The effect of the estrous cycle and estrogen on the release of immunoreactive alpha-melanocyte-stimulating hormone

Circulating levels and tissue content of alpha-MSH were measured on the morning of various days of the estrous cycle, and on the afternoon of proestrus in freely moving conscious rats. No surges of alpha-MSH were detected by RIA in the morning of various days of the cycle. The neurointermediate lobe content of alpha-MSH was slightly elevated on diestrus 1 as compared to the levels on diestrus 11 and proestrus but not to estrous levels. No changes in alpha-MSH content were detected in the anterior pituitary, the median eminence, mediobasal hypothalamus and the preoptic area at various stages of the estrous cycle. Plasma alpha-MSH levels were slightly elevated at 1500 hr of proestrus which was followed three hours later by a decline. This profile of plasma alpha-MSH on the afternoon of proestrus was reproduced by the SC administration of estradiol benzoate to long-term ovariectomized rats. These data suggest that, contrary to the results obtained by bioassay of alpha-MSH no surges of alpha-MSH occur on any day of the cycle, although a slight elevation on the afternoon of proestrus was detected. The altered pattern of release of this peptide on the afternoon of proestrus may be induced by estrogen.     

Gastric protection by alpha-melanocyte-stimulating hormone against ethanol in rats: involvement of somatostatin

The proopiomelanocortin-derived tridecapeptide alpha-melanocyte-stimulating hormone (alpha-MSH) is a neuropeptide that exerts broad anti-inflammatory actions in mammals. This study aimed to investigate the effect of alpha-MSH on ethanol-induced gastric ulcer in rats and to evaluate the involvement of endogenous somatostatin in the actions of the peptide. The rats received 1 mL 75% ethanol or saline orally. alpha-MSH was given (25 micro g/rat; i.p.) alone or following the somatostatin antagonist cyclo-(7-aminoheptanoyl-PH-E-d-Trp-Lys-THR) (10 microM/kg; i.p.) administration. Gastric lesions were scored macroscopically and microscopically following decapitation at 30 min after ethanol challenge. Gastric malondialdehyde (MDA) level, myeloperoxidase (MPO) activity and mast cell counts were assessed. Ethanol-induced gastric hemorrhagic lesions were characterized by increased gastric MDA level, MPO activity and mast cell counts. alpha-MSH treatment decreased the extent of tissue injury and reversed tissue MDA level, MPO activity and mast cell counts. The effect of the peptide on the severity of gastric lesions, MDA level and MPO activity was reversed by the somatostatin antagonist. In conclusion, alpha-MSH is beneficial in a rat model of gastric ulcer via mechanisms which partly involve the endogenous somatostatin.     

Interaction of alpha-melanotropin (alpha-MSH) and noradrenaline in the median eminence in the control of female sexual behavior

In the present study, we examined the effects of the injection of alpha-melanotropin (alpha-MSH), noradrenaline (NA), and dopamine in the median eminence of ovariectomized-adrenalectomized rats on female sexual behavior. The animals were primed with l0 microg of estradiol benzoate, and 52-54 h later they were injected into the median eminence with either 1 microl of artificial cerebrospinal fluid, 1 microg/rat alpha-MSH, 200 ng/rat NA, 200 ng or 2 microg/rat dopamine, in 1 microl of artificial cerebrospinal fluid. Both alpha-MSH and NA significantly stimulated sexual behavior. This effect was antagonized by two beta-adrenergic antagonists: propranolol (500 ng/rat) and metoprolol (400 ng/rat) applied 15 min before the alpha-MSH or NA. The alpha-adrenergic antagonist prazosine (500 ng/rat) was ineffective in reducing the effect of alpha-MSH. The vehicle and dopamine at both doses had no effect on sexual activity. These results indicate that alpha-MSH and NA in the median eminence stimulate female sexual behavior and that NA mediates the action of alpha-MSH via beta-receptors.     

Effect of 41-CRF antiserum on the secretion of ACTH, B-endorphin and alpha-MSH in the rat

In order to elucidate the physiological role of the 41 amino-acid residue corticotropin-releasing factor (41-CRF) on the secretion of ACTH, B-Endorphin and alpha-MSH, plasma levels of these peptides were measured by radioimmunoassay in intact and adrenalectomized rats, two hours after the injection of either 41-CRF antiserum (CRF-AS) or normal rabbit serum for controls. The administration of CRF-AS strikingly lowered the plasma ACTH levels in both intact and adrenalectomized rats. A statistically significant reduction of plasma levels of B-Endorphin was also observed in the same rats. However, the effect of CRF-AS on B-Endorphin release was less pronounced than the effect on ACTH release. No changes in plasma alpha-MSH levels were observed after passive immunization with CRF-AS. We conclude that, in the rat, 41-CRF plays a physiological role in the regulation of ACTH and B-Endorphin secretion, but is not involved in the regulation of alpha-MSH release from the pituitary gland.     

Dopaminergic control of aldosterone: modulation of the response of rat adrenal zona glomerulosa cells to alpha-Msh by pretreatment with bromocriptine or metoclopramide

Bromocriptine treatment in rats (3 mg/kg per day, 7 days) significantly reduced alpha-msh and aldosterone plasma levels 2 hrs after the final treatment in animals on low, normal and high sodium diets. Alpha-MSH dose response curves for corticosterone and 18-hydroxydeoxycorticosterone (18-OH-DOC) in subsequently incubated glomerulosa cells gave stimulation at lower concentrations of alpha-MSH (10(-10) moles per litre) than in cells from untreated animals (10(-9) moles per 1). Curves for aldosterone (ald) and 18-hydroxycorticosterone (18-OH-B) were also affected in cells from animals on a low sodium diet. Fasciculata-reticularis cell responses to ACTH were unaffected. Metoclopramide (4 mg/kg per day, 7 days) elevated plasma alpha-MSH, although ald was unaffected, but inhibited the glomerulosa cell response to alpha-MSH in vitro. Acute dopaminergic responses in plasma ald may be mediated through alpha-MSH in rats, but chronically alpha-MSH may down- regulate glomerulosa cell alpha-MSH receptors. It is unlikely that alpha-MSH mediates the adrenocortical response to sodium depletion.     

Anti-inflammatory effect of the alpha-melanocyte stimulating hormone in animal eyes undergoing extracapsular lens extraction

In this study anti-inflammatory effects of the alpha-melanocyte stimulating hormone (alpha-MSH) on ocular inflammation caused by extracapsular lens extraction (ECLE) have been investigated and the potential mechanism of an anti-inflammatory effect is discussed. Pigmented rabbit eyes after ECLE were treated locally with alpha-MSH, dexamethasone, diclofenac, or saline 4 times a day (q.i.d.) for 4 weeks. The inhibitory effect of alpha-MSH on infiltrating cells in the aqueous humor (AqH) was almost twice as good as that of dexamethasone or diclofenac for 3 days, 1 week, and 2 weeks after the operation. The eyes of Sprague-Dawley rats were treated with an intravenous injection of alpha-MSH or saline immediately after ECLE. Six hours postoperatively, the iris/ciliary body exhibited increased expression of TNF-alpha and IL-6 mRNAs, which were significantly decreased after alpha-MSH treatment. The number of activated NF-kappa B (NFkappaB)-positive cells in the iris/ciliary body was also significantly reduced by the alpha-MSH treatment. These results suggested that alpha-MSH could effectively reduce ocular inflammation after ECLE, and the potential mechanism for this is by down-regulating the expression of proinflammatory cytokines and inhibiting the NFkappaB-dependent signaling pathway.     

A hormone-sensitive stage in the development of the retinal pigment epithelium in Hunter rats with hereditary retinal dystrophy

The sensitivity of the retinal pigment epithelium (RPE) to the melanotropic effects of alpha-MSH and dbcAMP was assayed in an organ culture of the eye scleral part in the Hunter rats with inherited retinal dystrophy. The melanin synthesis was estimated by liquid scintillation on the RPE isolated enzymatically after 48-h cultivation. One eye from every animal was cultivated in a medium without natural components and with the hormone or dbcAMP (experiment), while the other in a hormone-free medium (control). The melanin synthesis was estimated by 14C-thiouracil incorporation. The result was expressed as a cpm/microgram DNA (experiment) to cpm/microgram DNA (control) ratio. In addition, the index of labelled nuclei was determined using 3H-thymidine autoradiography in the central RPE zone of the eyes from young rats of the same litter. The experiments with alpha-MSH confirmed the earlier data according to which the RPE of the 3 day old Hunter rats were insensitive to melanotropic hormones. This was not due to defects in the cytoplasmic melanin-synthesizing system, since under the influence of dbcAMP the melanin synthesis in the RPE increases more than four-fold as compared with the control; dbcAMP stimulates also the total protein synthesis, as estimated by 3H-leucine incorporation. The RPE of the 4 day old rats proved to be sensitive to alpha-MSH: the melanin synthesis increases more than twice suggesting the healthy state of the RPE membrane melanotropic receptors. alpha-MSH also stimulates the total protein synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of alpha-MSH on progesterone and nitric oxide release by cultured ovarian granulosa cells in experimental rat autoimmune oophoritis

The peptide alpha-melanocyte-stimulating hormone (alpha-MSH) occurs within the pituitary, brain, skin, ovary and other tissues, and has potent anti-inflammatory activity. For this reason, we examined its effects on an autoimmune disease: the experimental autoimmune-oophoritis (EAO). We analyzed the effect of the peptide on the release of nitric oxide (NO) and progesterone from cultured ovarian granulosa (GL) cells at 0, 7, 14, 21 and 28 days after sensitization of the rats. On day 0 the progesterone levels were higher in estrous rats than those in proestrus and diestrus. The NO amount did not differ among the diverse days of the cycles. The administration of alpha-MSH induced a decrease of NO in estrus and diestrus, but did not affect progesterone release. The EAO rats showed a period of constant diestrus ranging from about 7 to 14 days after immunization. At the onset (day 7) and the end of this period (day 14), the NO significantly increased in estrous rats which was correlated with a reduction in progesterone concentration. This effect was reverted by alpha-MSH. At 21 and 28 days, progesterone release increased only when the rats were in proestrus, while NO production was similar to that on day 0. Administration of alpha-MSH reduced progesterone release when the rats were in proestrus and these results were correlated with an increase in NO only at day 14. The results obtained suggest that alpha-MSH could act as a modulator of EAO, specially when the rats are in estrus.     

Paraventricular hypothalamic alpha-melanocyte-stimulating hormone and MTII reduce feeding without causing aversive effects

alpha-Melanocyte-stimulating hormone (alpha-MSH) appears to play a tonic inhibitory role in feeding and energy storage. MTII, a specific synthetic MC3-R/MC4-R agonist, has similar effects on feeding in rats. The current studies demonstrate that PVN administration of alpha-MSH or MTII decreases nocturnal and NPY-stimulated food intake without causing aversive effects. Co-administration with NPY of 600 pmol alpha-MSH or 1 pmol MTII into the PVN caused a significant decrease in NPY-induced feeding. PVN administration of MTII or alpha-MSH at doses effective to suppress feeding did not cause conditioned taste aversion (CTA). ICV administration of alpha-MSH, however, did cause weak CTA. These results indicate that the potent effects on feeding of MC3-R and MC4-R agonists when injected into the PVN are not due to aversive effects.     

Changes in hypothalamic agouti-related protein (AGRP), but not alpha-MSH or pro-opiomelanocortin concentrations in dietary-obese and food-restricted rats.

Melanocortin-4 receptor (MC4-R) density is thought to be regulated by synaptic availability of endogenous agonist, alpha-melanocyte-stimulating hormone (alpha-MSH), and also by agouti-related protein (AGRP), which acts as a competitive antagonist. As hypothalamic MC4-R have been implicated in the regulation of energy balance, we examined concentrations of alpha-MSH and AGRP in hypothalami of dietary-obese and food-restricted rats. In dietary-obese rats, AGRP concentrations were significantly increased by 43% (p < 0.01) above lean controls, whereas a 91% (p < 0.01) reduction was observed in food-restricted rats. Surprisingly, hypothalamic concentrations of alpha-MSH and its precursor peptide, pro-opiomelanocortin (POMC), did not differ significantly from controls in either model. In conclusion, we suggest that MC4-R activity may not be regulated by changes in agonist (alpha-MSH) but by changes in the antagonist (AGRP) availability, which may modulate background activation of the receptor by tonic alpha-MSH release. AGRP may be an important modulator of feeding behaviour.     

Central alpha-MSH,energy balance,thermal balance,and antipyresis

Intracerebroventricular administration of alpha-MSH in young adult rats enhanced metabolic rate and caused a dose-dependent suppression of food intake, exhibiting a coordinated catabolic pattern. However, the thermoregulatory effects did not seem to be coordinated: the rising heat production was accompanied by a practically simultaneous tendency for rise in heat loss (skin vasodilatation), and the final core temperature either increased or decreased depending on which rise prevailed. The effect on heat loss possibly explains the antipyretic properties of the peptide.     

Suppression of basal and stress-induced prolactin release and stimulation of luteinizing hormone secretion by alpha-melanocyte-stimulating hormone

alpha-MSH and beta-endorphin, both synthesized from a common precursor, have opposite behavioral actions. In order to determine if these peptides have opposite effects on pituitary function, basal LH secretion and basal and stress-induced prolactin release were studied in adult male rats after intraventricular injection of alpha-MSH. Each rat also received intraventricular saline in order to serve as its own control. 18 micrograms alpha-MSH stimulated plasma LH from 16.5 +/- 2.5 (SEM) ng/ml to a peak of 27.2 +/- 4.0 and 26.0 +/- 4.9 ng/ml at 5 and 10 min, and suppressed prolactin from 3.5 +/- 0.7 ng/ml to 1.3 +/- 0.1 and 1.2 +/- 0.1 ng/ml at 15 and 30 min. Intraventricular alpha-MSH also significantly blunted the prolactin rise associated with the stress of swimming. 10 and 20 min after the onset of swimming, prolactin levels in rats pretreated with alpha-MSH were significantly diminished: 7.4 +/- 1.5 and 6.5 +/- 2.0 ng/ml vs 23.8 +/- 3.6 and 15.2 +/- 2.8 after normal saline. Similarly, des-acetyl alpha-MSH which is the predominant form of alpha-MSH in the hypothalamus, diminished the stress-induced prolactin rise from 18.4 +/- 5.3 and 11.2 +/- 3.4 ng/ml at 10 and 20 min to 10.0 +/- 2.4 and 5.5 +/- 1.6 ng/ml. We conclude that centrally administered alpha-MSH stimulates LH and suppresses basal and stress-induced prolactin release in male rats. These actions are opposite to those previously shown for beta-endorphin and suggest that alpha-MSH may antagonize the effects of beta-endorphin on pituitary function.     

Alpha-melanocyte-stimulating hormone exhibits target cell selectivity in its capacity to affect interleukin 1-inducible responses in vivo and in vitro

The ability of i.v.-administered recombinant human interleukin 1 (IL 1 beta) to increase core body temperature, stimulate an increased production of serum amyloid P substance, and augment blood levels of circulating neutrophils in mice was inhibited in a dosage-dependent manner by administration of the neuropeptide alpha-melanocyte-stimulating hormone (alpha-MSH). alpha-MSH administration was also capable of inhibiting the capacity of i.v.-administered IL 1 beta to enhance plasma levels of corticosterone and to depress the generation and/or elicitation of contact hypersensitivity responses to skin-reactive chemicals. An analog of alpha-MSH (Nle4, D-Phe7 alpha-MSH), known to be more potent than native alpha-MSH in a number of melanotropin-sensitive systems, was determined to be more active than alpha-MSH in the modification of these same in vivo responses. Neither alpha-MSH nor its analog were capable of altering the capacity of IL 1 to stimulate increased plasma levels in prostaglandin E2 (PGE2). In vitro, neither alpha-MSH nor its analog were capable of reducing the capacity of IL 1 to stimulate fibroblast production of PGE2 or to augment the proliferation of murine thymocytes exposed to phytohemagglutinin. The apparent selectivity associated with the regulatory influences of alpha-MSH on IL 1-induced responses in vivo suggests that this neuropeptide may function as an endogenous inhibitor of certain immunomodulatory and inflammatory activities of the cytokine IL 1.