In two separate experiments, the gonadal response to melatonin treatment and exposure to continuous white light (LL) and different spectra of light (blue, green, yellow and red) was investigated in the Indian desert gerbil Meriones hurrianae. In experiment 1, exposure to green light for 8 weeks increased (p < 0.01) the gonadosomatic index (GSI) and sperm count, whereas exposure to red light decreased (p < 0.01) the GSI and sperm count. The response of accessory organs to the treatment varied. In experiment 2, exposure to LL for 5 weeks decreased the GSI and sperm count, and treatment with melatonin (in the late-light period) not only increased the GSI and sperm count, but also counteracted the inhibitory action of LL and red light. Melatonin treatment stimulated accessory sex organs and the scent gland surface area. The inhibition or stimulation of the reproductive parameters correlated with an increase or decrease in pinealocytes and pinealocyte nuclear diameters. Therefore, the influence of light and its spectra on reproduction may be mediated by the pineal gland, though extrapineal mechanisms cannot be ruled out.

Animals↗

PubMedDate not supplied

Effect of exposure to continuous light and melatonin on ovarian follicular kinetics in the skipper frog, Rana cyanophlyctis.

Ovarian follicular kinetics and gravimetric changes in the ovary and oviducts were studied in the skipper frog, Rana cyanophlyctis, following exposure to continuous light and melatonin treatment during the breeding season. Daily late-afternoon injections of melatonin (15 micrograms subcutaneous) for 30 days decreased the gonadosomatic index (GSI), whereas continuously available melatonin from subcutaneous implants did not influence the GSI compared to those of controls. Exposure to continuous light for 30 days stimulated the GSI, and melatonin given as daily injections prevented the continuous-light induced increase in GSI. Oviductal weights decreased only in the melatonin-injected groups. Data on follicular kinetics revealed a decrease in first-growth-phase (FGP) oocytes and an increase in medium-sized second-growth-phase (MSGP) and large-sized second-growth-phase (LSGP) oocytes following continuous-light exposure. Melatonin administered to continuous-light-exposed frogs did not change the FGP oocyte number; however, it reduced both the MSGP and LSGP oocytes. Melatonin administration to frogs held in a light and dark cycle increased FGP oocytes and decreased MSGP and LSGP oocytes. Atretic follicles increased in all melatonin-treated groups. The results suggest that continuous light stimulates and melatonin inhibits reproductive function in this species.

Animals↗

PubMedDate not supplied

Diurnal sensitivity in melatonin-induced hematological changes in the male albino rat.

The influence of melatonin on diurnal changes in the hematological profile was investigated in male albino rats. Following treatment with melatonin, under two different experimental protocols, blood samples were collected at 06.00, 12.00, 18.00 and 24.00 h from separate groups of animals for detailed hematological analysis. In experiment 1, melatonin (25 micrograms, s.c.) treatment, once daily at 17.00 h for 4 weeks, led to an alteration in the rhythm of RBC production with a decrease in its counts at 12.00 h. The total WBC counts were increased at 06.00 and 12.00 h and decreased at 18.00 and 24.00 h. In experiment 2, twice-daily administration of melatonin (once at 09.00 h and again at 17.00 h), for 2 weeks, resulted in a decrease in total RBC counts at 06.00 and 24.00 h, whereas at 18.00 h there was an increase, compared to the respective control values. The total WBC counts increased at 06.00, 12.00 and 18.00 h and decreased at 24.00 h. Erythrocyte indices like mean cell volume (MCV), mean cell hemoglobin (MCH) and mean cell hemoglobin concentration (MCHC), in both experiments, correlated with RBC, hemoglobin and hematocrit values. The WBC differential counts in experiment 1 revealed a decrease in total neutrophils at 24.00 h, whereas in experiment 2 there was a general decrease in their number. While in experiment 1 the total lymphocyte number was increased at 06.00 h and decreased at 18.00 and 24.00 h, in experiment 2 it was increased except at 24.00 h. It may be concluded that melatonin has a modulatory role in hemopoiesis and its rhythms. The stimulatory effect of melatonin on WBC supports its purported immunopotentiating action.

Animals↗

PubMedDate not supplied

Thermotrophic effect of melatonin in adrenalectomized and thyroidectomized rats.

A single injection of 25 micrograms melatonin induced hyperthermia in rats. The mechanism(s) by which melatonin induces hyperthermia is not clear. In this study the thermotrophic effects of melatonin were studied in adrenalectomized (ADX) and thyroidectomized (TX) rats to ascertain if melatonin-induced hyperthermia is mediated through these glands, as both these glands play a significant role in mammalian thermoregulation. Melatonin (25 micrograms) was administered as a single subcutaneous injection at 06.00, 12.00, 18.00, and 24.00 h. Body temperatures were recorded, using an anal thermometer at hourly intervals, round the clock. In the scotophase the animals were located using dim red light and injected. Although the administration of melatonin to both intact and ADX rats resulted in a rise in body temperature, the effect was more pronounced in the former compared to the latter group. Melatonin induced hyperthermia only during the photophase of the diurnal cycle; in the scotophase the response was either poor or nil. In TX rats melatonin was ineffective in inducing hyperthermia in either the photophase or scotophase. The body temperatures of TX rats and melatonin-injected TX rats were parallel. The results indicate that in ADX rats melatonin induced minor hyperthermia, whereas in TX animals it failed to produce any hyperthermia. The findings suggest that melatonin induces hyperthermia probably through its action on thyroid activity. Other mechanisms of action cannot be ruled out, however.

Adrenalectomy↗

PubMedDate not supplied

Melatonin in the control of the estrous cycle of the Indian desert gerbil (Meriones hurrianae: Jerdon).

Daily administration of melatonin for 8 weeks, either in the morning (9 a.m.) or late in the afternoon (5 p.m.), resulted in significant prolongation of the estrous cycle in the Indian desert gerbil Meriones hurrianae. The gonadosomatic index increased significantly (p < 0.01) in the melatonin-treated gerbils compared to the control animals. Histological study of the ovaries revealed enlargement of follicles and corpora lutea with hypertrophied granulosa cells in the melatonin-treated gerbils in comparison to their controls. The data suggest that the mechanism involved in the gonadal response to melatonin may not be the same in the temperate and tropical species.

Animals↗

PubMedDate not supplied

"Hepatitis "B" antigen in voluntary blood donors in Miraj area".

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Adolescent↗