Cyclic adenosine 3',5'-monophosphate content and bronchial smooth muscle contractility of hyper- and hypothyroid lungs.

1. Male Sprague-Dawley rats were made either hyper- or hypothyroid with thyroxine or 4-methyl-2-thiouracil, respectively. Bronchial smooth muscle (BSM) contractility and lung cyclic adenosine 3',5'-monophosphate (cAMP) content were measured in both conditions. 2. Bronchial smooth muscle contractility was significantly weaker in hyperthyroid rats, while the BSM contractility of hypothyroid rats was the same as controls. 3. The cAMP content of hyperthyroid rat lungs was similar to controls but was decreased in hypothyroid rats. 4. These studies demonstrated that both the hyper- and hypothyroid states affect respiration, although the mechanisms involved with different for each condition.

Effects of steroid hormones on cyclic adenosine 3',5'-monophosphate levels in the rat lung.

The possible role of cyclic adenosine 3',5'-monophosphate (cAMP) in mediating the action of steroid hormones was investigated using the rat lung. Male rats were adrenalectomized and treated with olive oil, dexamethasone, corticosterone, deoxycorticosterone (DOC) or progesterone. At the end of 10 days, 100 micrograms isoprenaline/kg was injected intraperitoneally 5 min before the animals were killed to stimulate cAMP production. Adrenalectomy significantly decreased cAMP levels in the rat lung. Dexamethasone and corticosterone pretreatment reversed the effect of adrenalectomy whereas progesterone pretreatment but not DOC pretreatment significantly decreased lung cAMP levels. Cyclic AMP levels in normal female rats, whether pregnant or not, were not significantly different from those in male rats. We concluded that the absence of glucocorticoid, as after adrenalectomy, decreased the cAMP levels in rat lungs and that this could be reversed by either dexamethasone or corticosterone replacement. Progesterone reduced the cAMP content in rat lungs by acting as a glucocorticoid antagonist or by acting directly via progesterone receptors.

Effects of steroid hormones pretreatment on isoprenaline-induced cyclic adenosine 3',5'-monophosphate in rat lung.

1. Steroid hormones have been shown to regulate the concentration of adrenergic and muscarinic receptors in many tissues. 2. The cyclic adenosine 3',5'-monophosphate (cAMP) content in rat lung tissues in response to either dexamethasone, corticosterone, deoxycorticosterone or progesterone for 7 days were measured following intraperitoneal injection of isoprenaline just before sacrificed. 3. There was a significant increase in cAMP level (P less than 0.001) in dexamethasone and corticosterone-treated rats compared to controls that received isoprenaline alone. 4. Pretreatment with deoxycorticosterone and progesterone suppressed the increase in cAMP in response to isoprenaline. 5. The effect of glucocorticoids in causing bronchodilatation in asthmatic patients is partly due to the restoration of adenyl cyclase responsiveness to beta-agonist.

The effect of corticosteroid pretreatment in vivo on the contraction of guinea-pig ileum and duodenum.

The effects of corticosteroid pretreatment on the contraction caused by acetylcholine or electrical stimulation of guinea-pig ileum and duodenum were studied. The acetylcholine dose-response curves for steroid pretreated ileum but not duodenum were significantly shifted to the right; evidence that pretreated ileum required higher dose of acetylcholine than normal to cause 50% maximal contraction. Naloxone enhanced the contraction of normal ileum caused by acetylcholine given at the dose of ED50, but not that of normal duodenum. The dose of morphine required to abolish electrically induced contraction was higher in steroid pretreated ileum than in normal ileum. Hence, corticosteroid pretreatment may affect intestinal contractility via opioidergic mechanisms which are found in the ileum but not in the duodenum.