ABSTRACT
1. 5-HT inhibits spontaneous fluid secretion as well as stimulated secretion with secretin (cAMP mediated) or ACh (Ca2+ mediated) in the isolated guinea pig pancreatic ducts. 2. The inhibitory effect of 5-HT is reversible and is dependent on the concentration in the range 0.01-0.1 microM, which is much lower than those that affect intestinal motility and secretion. 3. The 5-HT3 receptor in duct cells appears to mediate the inhibitory effect of 5-HT. 4. [Ca2+]i is unlikely to mediate the inhibitory effect of 5-HT.
Subject(s)
5-Methoxytryptamine/pharmacology , Acetylcholine/pharmacology , Animals , Calcium/metabolism , Guinea Pigs , Pancreatic Ducts/metabolism , Pancreatic Ducts/drug effects , Secretin/pharmacology , Serotonin/pharmacology , Serotonin/metabolism , Serotonin/analogs & derivatives , Vasodilator Agents/pharmacologyABSTRACT
Effects of late afternoon injections of different doses of melatonin (aMT) and 5-methoxytryptamine (MT) were studied on the testes in sham operated (SO) and pinealectomized (Px) F. pennanti during various reproductive phases. 5-methoxyindoles (MI) in doses 10 and 50 micrograms given for 60 continuous days reduced the weight and activity of the testes in SO and Px animals during the active and regressive phases. During the inactive phase MI administration caused an inhibitory influence on the testes of Px animals. However, during the recrudescence phase no significant effect of MI injections was visible. Both aMT and MT injected for 20 and 40 days respectively failed to influence the testes significantly. Also 1 microgram of the MI had no effect. The results suggest a reproductive phase dependent effect of aMT and MT on the testes of this tropical rodent. The dose and duration of administration are critical and their effects are independent of the pineal gland.
Subject(s)
5-Methoxytryptamine/pharmacology , Animals , Male , Melatonin/pharmacology , Periodicity , Pineal Gland/drug effects , Sciuridae/physiology , Seasons , Testis/drug effectsABSTRACT
The present study reveals that the annual Harderian gland weight cycle of P. asiatica has a direct relationship with the testicular cycle and an inverse relationship with the pineal gland cycle. Pinealectomy resulted in a significant decrease of the Harderian gland weight during the recurdescence (March-May) and active (April-June) phases. Subcutaneous implantation of melatonin (aMT) and 5-methoxytryptamine (MT) brought about a significant reduction during the recrudescence and active phases whereas subcutaneous injections of aMT, MT and 5-methoxytryptophol (ML) reduced Harderian gland weight effectively during the morning as well as in the evening hours in the active and inactive phases.