Effect of melatonin treatment on 24‐hour rhythms of serum ACTH, growth hormone, prolactin, luteinizing hormone and insulin in rats injected with Freund's adjuvant

Abstract

The effect of melatonin injection on Freund's adjuvant-induced changes in levels and 24-hr rhythms of circulating ACTH, growth hormone (GH), prolactin (PRL), luteinizing hormone (LH), and insulin was assessed in rats. Animals received subcutaneous (s.c.) injections of melatonin (30 microg) or vehicle, 1 hr before lights off for 12 days. Ten days after melatonin treatment, they were injected with Freund's complete adjuvant or its vehicle s.c., and after 3 days, rats were killed at six different time intervals throughout a 24-hr cycle to measure the different hormones by radioimmunoassay (RIA). Following Freund's adjuvant injection, an increase in serum ACTH, with maintenance of ACTH diurnal rhythm was found. Acrophases of the ACTH rhythm varied from 13:39 to 17:12 hr and the amplitude of rhythm was augmented after immunization. In immunized rats, melatonin treatment increased the amplitude of serum ACTH rhythm. For GH, a depressive effect of immunization on circulating levels, together with absence of diurnal rhythmicity were found. Immunization augmented circulating PRL, while conserving its diurnal rhythmicity. Melatonin-injected rats showed significant diurnal variations of serum PRL after immunization only. Acrophases of the serum PRL rhythm varied from 19:37 to 22:04 hr. Immunization decreased circulating LH and suppressed its 24-hr rhythmicity pattern. The effect of immunization on LH was counteracted by melatonin injection. Acrophases of serum LH rhythm varied from 00:44 to 03:53 hr. Significant effects of immunization and time of day on circulating insulin were detected; immunization increased serum insulin levels with a shift in acrophase from early afternoon to midnight. The data indicate that several early changes in levels and 24-hr rhythms of circulating ACTH, PRL, and LH in Freund's adjuvant-injected rats were sensitive to treatment with pharmacological amounts of melatonin.

Long-term melatonin administration attenuates low-LET γ-radiation-induced lymphatic tissue injury during the reproductively active and inactive phases of Indian palm squirrels (Funambulus pennanti)

“…This protective effect of SOD might be explained by correlating its activity pattern with the seasonal variation in internal melatonin level of F. pennanti [16]. The effects of melatonin on the levels of a number of biochemical variables, on hormones and on oxidative and antioxidative status in mammals, and how they change in relation to their circadian patterns, have been reported [47,48]. Besides being a circadian and seasonal biorhythm regulator, a wide spectrum of targets and effects of melatonin has evolved in a variety of tissues, such as the gut, cerebrospinal fluid, ovary, skin, bone marrow, bile fluid and lymphocytes, as well as in whole organisms [49][50][51][52][53][54][55].…”

Effect of Interferon-γ Treatment on 24-Hour Variations in Plasma ACTH, Growth Hormone, Prolactin, Luteinizing Hormone and Follicle-Stimulating Hormone of Male Rats

“…Sensitivities of RIAs were 0.2, 0.04, 0.045, 0.097 and 0.048 ng/ml using the NIDDK rat ACTH-RP-1, rat GH-RP-2, rat prolactin RP-3, rat FSH-RP-2 and rat LH-RP-3, respectively. Results were expressed as pg/ml of plasma [25,[27][28][29] .…”

Effect of melatonin on biochemical variables of the blood in dairy cows

“…For this reason melatonin may affect -directly or indirectly -the metabolism of a given organism (Vanecek, 1998;Maćkowiak et al, 1999a, b). The advantageous effects of melatonin on carbohydrate-lipid metabolism (Maćkowiak et al, 1999a, b;Hoys et al, 2000) as well as on the endocrine status (Maćkowiak et al, 1999a;Esquifino et al, 1999;Fabiś et al, 2002) have already been demonstrated.…”