Relationship between prostagandin E1, polyphloretin phosphate and alpha and beta adrenoceptor-bound feeding loci in the hypothalamus of sheep

Prostaglandins and hypothalamic neurotransmitter receptors involved in hyperthermia: a critical evaluation

The role of a prostaglandin of the E series (PGE) in the hypothalamic mechanisms underlying a fever continues to be controversial. This paper reviews the historical literature and current findings on the central action of the PGEs on body temperature (Tb). New experiments were undertaken to examine the local effect of muscarinic, nicotinic, serotonergic, alpha-adrenergic, or beta-adrenergic receptor antagonists at hypothalamic sites where PGE1 caused a rise in Tb of the primate. Guide tubes for microinjection were implanted stereotaxically above sites in and around the anterior hypothalamic, preoptic area (AH/POA) of male Macaque monkeys. Following postoperative recovery, 30-100 ng of PGE1 was micro-injected unilaterally in a volume of 1.0-1.5 microliter at sites in the AH/POA to evoke a rise in Tb, and once identified, pretreated with a receptor antagonist. PGE1 hyperthermia was significantly reduced by microinjections of the muscarinic and nicotinic antagonists, atropine, or mecamylamine, at PGE1 reactive sites in the AH/POA. The serotonergic antagonist, methysergide, injected at PGE1 sensitive sites in the ventromedial hypothalamus also attenuated the rise in Tb. However, the 5-HT reuptake blocker, fluoxetine, and the beta-adrenergic receptor antagonist, propranolol, injected in the AH/POA failed to alter the PGE1 hyperthermia. In contrast, the alpha-adrenergic antagonist, phentolamine, potentiated the increase in Tb at all PGE1 reactive sites in the hypothalamus. An updated model is presented to explain how the concurrent actions of aminergic neurotransmitters acting on their respective receptors in the hypothalamus can interact with a PGE to elicit hyperthermia. Finally, an evaluation of the current literature including recent findings on macrophage inflammatory protein (MIP-1) supports the conclusion that a PGE in the brain is neither an obligatory nor essential factor for the expression of a pyrogen fever.

Influence of polyphloretin phosphate on the central effects of prostaglandin E2 and F2alpha in rats

The possibility that polyphloretin phosphate (PPP) antagonizes the central effects elicited by prostaglandin (PG) E2 and F2alpha was investigated. PPP was administered i.c.v. to male Wistar rats (10 or 25 microgram) 10 or 30 min before i.c.v. injection of PGF2 or PGF2alpha (1 or 10 microgram). The duration of several component of behavior, the degree of irritability, and the rectal temperature of rats were measured; the levels of noradrenaline, dopamine, 5-hydroxytryptamine, and 5-hydroxyindoleacetic acid were measured spectrophoto-fluorometrically in discrete brain areas. PPP antagonized temperature and behaviroal changes induced in rats by PGF2alpha, but not those induced by PGE2. The magnitude of antagonism depended on the dose of PPP and on the time of the pretreatment before PGF2alpha administration. Changes in the level of biogenic amines in discrete brain areas evoked by PGs were not affected by PPP. We found that PPP antagonizes the central effects of PGF2alpha but not those of PGE2, and that changes of biogenic amines in discrete brain areas elicited by PGs are not specific.

Effect of indomethacin on water intake of the rat

Indomethacin stimulated water intake in intact rats. This effect could also be demonstrated in bilaterally ureteral ligated rats, but it was totally abolished after bilateral nephrectomy. It is suggested that the stimulatory effect of indomathacin on water consumption is mediated by a renal factor.

Some observations on the anorectic activity of prostaglandin F2alpha

1 Intracerebroventricular injection of prostanglandin F2alpha (10-40 microgram) decreases food intake in a dose-dependent manner in rats trained to consume their daily total food intake in a 2 h period. 2 This anorexia is also observed in satiated rats, which had ad libitum access to food. 3 The anorectic activity of prostaglandin F2alpha is not modified by changes in the internal environment of the body after food intake, such as increased blood glucose and insulin levels and decreased fatty acid levels, or by the presence or absence of food in the stomach, as is evident from the anorectic activity of prostaglandin F2alpha in partially satiated rats. 4 The anorexia is not due to pain or irritative properties of prostaglandin F2alpha since induction of comparable pain with 3% acetic acid does not affect food intake in rats deprived of food for 22 hours. 5 Anorectic doses of prostaglandin F2alpha when injected intraperitoneally cause hypothermia. 6 The results suggest that the inhibitory activity of prostaglandin F2alpha on food intake is at both peripheral and central sites. 7 Prostaglandin F2alpha-induced anorexia is associated with the behavioural tranquilization that is seen after the ingestion of food.

Feeding and temperature changes in sheep following injections of barbiturates, Ca-++, or Mg-++ into the lateral, third, or fourth ventricle or cerebral aqueduct

Eleven sheep were prepared with cannula guides directed toward four areas within the ventricular system to determine effective sites of action of chemicals which when injected into the cerebrospinal fluid produce changes in feeding behavior and temperature regulation. Pentobarbital, barbital, calcium chloride, and magnesium chloride elicited feeding in sheep when injected into the third ventricle or into the cerebral aqueduct; however, feeding response was less after injections into the latter. Pentobarbital and magnesium chloride elicited an increase in body temperature when injected into the third ventricle but not when injected into the cerebral aqueduct. Perfusions (push-pull) of the lateral and third ventricles with calcium chloride and magnesium chloride solutions (50 mM) resulted in feeding while similar perfusions of the fourth ventricle resulted in no response. Responses to lateral and third ventricular injections presumably involved effects on both anterior and posterior hypothalamic areas while injections into the cerebral aqueduct, due to the caudal flux of the cerebrospinal fluid, may have affected primarily only the posterior hypothalamus and more caudal structures. The feeding response probably resulted from depression of neural fibers which inhibit feeding.

Feeding following intrahypothalamic injections of calcium and magnesium ions in sheep

To study ionic effects on hypothalamic control of feeding, seven sheep were each prepared with six bilateral medial-hypothalamic guides. Hypothalamic loci were identified where feeding resulted following 1 mu 1 injections of calcium chloride and/or magnesium chloride. Doses of 1 and 2 mumol were most effective to induce feeding, and potassium chloride was not effective. Injections of phentolamine, LB-46, carbachol, atropine, or prostaglandin E1 did not inhibit the feeding responses following magnesium chloride injections into magnesium ion responsive loci. Feeding following calcium chloride injections into calcium ion responsive loci was blocked by atropine and reduced by phentolamine. Carbachol and prostaglandin E1 elicited feeding when injected into magnesium but not calcium ion responsive loci. Injections of carbachol followed by magnesium chloride resulted in greater feeding than when either chemical was injected alone. Calcium and/or magnesium ion bound feeding loci were in the anterior, ventromedial, dorsomedial, posterior and lateral hypothalamus, and the mammillary bodies. These ions elicited feeding in sheep perhaps by decreasing excitability of feeding-inhibitory neural pathways in the hypothalamus.