Uterine adenylate cyclase activity during the estrous cycle and early progestation in the rat: responses to fluoride activation and decidual induction

Uterine adenylate cyclase (AC) activity of the rat was measured by radiochemical analysis during the estrous cycle and early pseudopregnancy. During the estrous cycle, AC activity increased from 4.6 to 16.9 pmol cAMP formed/min X mg protein between metestrus and proestrus. Although AC was activated 2- to 3-fold at all cycle stages by 10 mM NaF, the resulting pattern of activity was similar to that measured in the absence of fluoride. The results demonstrated that the pattern of AC activity during the cycle was similar to that of other estrogen-sensitive uterine enzymes and that the ovarian hormones probably altered enzyme biosynthesis and turnover to a greater extent than activation and kinetic properties. Following the induction of pseudopregnancy by cervical stimulation, enzymic activity increased from 3.5 to 9.4 pmol between Days 1-4 (Day 1=leukocytic vaginal smear) and declined thereafter. AC activity was increased 2- to 5-fold by NaF on all days. AC activity was similarly increased by a mechanical trauma to the uterus, but only when the trauma was applied on Day 4. Following trauma to the uterus, AC activity was not increased further by NaF. The similarities between the physicochemical characteristics of AC during the estrous cycle and early progestation suggested that the enzyme during all endocrine states had virtually identical properties. However, the transient sensitivity to activation after trauma on Day 4 was unique to progestational uteri. Because the properties of enzyme were not altered by the endocrine state of the tissue, the transient sensitivity to activation by trauma was suggested to be a result of hormone-induced alterations in the membrane in which AC is sequestered.     

Failure to demonstrate rat hippocampus adenylate cyclase

Summary The fate of ATP exposed to rat hippocampal extracts was investigated after their separation by a microdisc electrophoresis technique. It could be demonstrated that the histochemical adenylate cyclase procedure using ATP as substrate is not suitable for specific localization of the enzyme, since other ATP hydrolysing enzymes were also able to convert ATP unless the concentrations of inhibitors reached 1 mM (ouabain) and 40 mM (NaF). With a prolonged incubation time of 18 h further substrate splitting protein zones could be revealed, possibly reflecting activities of enzymes involved in the hydrolysis of degradation products of ATP.Supported by Ministerium für Hoch- und Fachschulwesen der DDR     

Modulation of muscarinic receptor-mediated adenylate cyclase and phospholipase C responses in rat retina

1. Agonist activation of rat retina muscarinic receptors results in suppression of cyclic AMP (cAMP) generation and enhanced phosphoinositide hydrolysis. 2. Pharmacological manipulations that elevate cAMP or stable analogues of cAMP attenuate the acetylcholine (ACh)-induced enhancement of phosphoinositide hydrolysis. We postulate that cross-talk between adenylate cyclase and phospholipase C signal transducing systems probably exists in rat retina, as has been described for other systems. 3. Intraocular administration of pertussis toxin attenuated the response of both adenylate cyclase and phospholipase C to muscarinic stimulation, suggesting that some retinal muscarinic receptors are apparently coupled to their effector systems via pertussis toxin sensitive G proteins.     

Dopamine-inhibited adenylate cyclase in female rat adenohypophysis

A dopamine-inhibited adenylate cyclase has been demonstrated in anterior pituitary gland of adult female rats, lactating and not lactating. This inhibitory effect was completely GTP dependent. In contrast, in the adenohypophysis of male rats, dopamine had no detectable effect on adenylate cyclase activity. In female rats the inhibition of the enzyme appears mediated by specific dopaminergic receptors: the effect of dopamine was mimicked by the dopaminergic agonists apomorphine and the ergot derivative CH 29–717, while norepinephrine was much less potent. On the other hand, the dopaminergic antagonists trifluoperazine and sulpiride competitively antagonized the dopamine inhibition of the adenylate cyclase. The possibility that the dopamine-inhibited enzyme is located in mammotrophs appears supported 1) by its observation in the female rat pituitary, which contains this type of cells in much larger proportion than the male gland (33–38% vs. < 5%); 2) by the pharmacological similarity between the dopaminergic receptors mediating the adenylate cyclase inhibition (this work) and those regulating prolactin release (which have been characterized in previous studies). The well known inhibition of prolactin release brought about by dopamine could therefore be mediated, at least in part, by a decrease in the intracellular level of cAMP.     

Vasopressin affects adenylate cyclase activity in rat brain: a possible neuromodulator

The effect of vasopressin on adenylate cyclase activity was measured in the homogenates of selected rat brain regions. Adenylate cyclase activity in homogenate of the caudate nucleus did not change significantly with various concentrations of vasopressin. Furthermore, vasopressin did not reliably alter adenylate cyclase activity in various brain regions. Vasopressin in low concentrations significantly enhanced the activation of caudate adenylate cyclase activity by dopamine. This effect of vasopressin was dose dependent. Maximal enhancement by vasopressin occurred at 100 microM vasopressin. These results indicate that vasopressin may not have a direct effect on brain adenylate cyclase activity but appears to modulate the action of dopamine on brain adenylate cyclase.     

Beta-adrenergic receptor-linked adenylate cyclase in rat posterior pituitary

A specific β-adrenergic-stimulated cyclic AMP generating system has been evidenced in rat posterior pituitary. This is clearly demonstrated by: 1) the adenylate cyclase (AC) affinity for stimulants was in the order ISO > NA > DA, and 2) propranolol, a specific β-adrenergic receptor blocker, was the only antagonist of the system. Clonidine and apomorphine were completely inactive, thus excluding an α-adrenergic and/or dopaminergic component in this AC system. Our data also indicate that dopaminergic receptors present in both pituitary lobes are not coupled to an AC.     

Multiple localizations of adenylate cyclase in rat hippocampus

Summary A new method for the histochemical demonstration of adenylate cyclase activity, introduced and biochemically tested by Poeggel et al. (1981a), was employed in nervous tissue. Using this method a multiple pattern of activity was detectable. Activity occurs in nervous as well as glial elements. Biochemical results and physiological conclusions could be confirmed by ultrahistochemical visualization of adenylate cyclase activity in nervous tissue. The specificity of the reaction is controlled by a number of variations of the incubation methods.     

Activation of adenylate cyclase system in the preconditioned rat heart

Ischemic preconditioning (IP) protects the heart against subsequent prolonged ischemia. Whether the beta-adrenoceptor/adenylate cyclase pathway contributes to this cardioprotection is not yet fully known. Using enzyme catalytic cytochemistry we studied the adenylate cyclase activity and its distribution in the preconditioned rat heart. Adenylate cyclase activity was examined in Langendorff-perfused rat hearts subjected to the following conditions: control perfusion; 30 min regional ischemia; 5 min occlusion and 10 min reperfusion (IP); IP followed by ischemia. Ischemia-induced arrhythmias and the effect of ischemic preconditioning on the incidence of arrhythmias were analyzed. At the end of experiment the heart was shortly prefixed with glutaraldehyde. Tissue samples from the left ventricle were incubated in a medium containing the specific substrate AMP-PNP for adenylate cyclase and then routinely processed for electron microscopy. Adenylate cyclase activity was cytochemically demonstrated in the sarcolemma and the junctional sarcoplasmic reticulum (JSR) in control hearts, while it was absent after test ischemia. The highest activity of the precipitate was observed after ischemic preconditioning. In the preconditioned hearts followed by test ischemia, adenylate cyclase activity in the precipitate was preserved in sarcolemma and even more in JSR. Protective effect of ischemic preconditioning was manifested by the suppression of severe arrhythmias. These results indicate the involvement of the adenylate cyclase system in mechanisms underlying ischemic preconditioning.     

Two types of hormone-responsive adenylate cyclase in the rat liver

We have demonstrated the existence of two types of hormone-responsive adenylate cyclase in the isolated perfused rat liver. One, less abundant, is linked to glycogenolysis and the other is not. Glucagon stimulates mainly the glycogenolysis-linked fraction and, to a lesser extent, the fraction which is not linked to glycogenolysis. The suppressive effect of insulin is specific for the glucagon-responsive adenylate cyclase and is inhibited by 3-isobutyl-1-methylxanthine (IBMX). However, this mechanism can explain only partly the ability of insulin to suppress glycogenolysis, and is not observed when cAMP is increased sufficiently by glucagon. Secretin-responsive adenylate cyclase is not linked to glycogenolysis and is suppressed specifically by oxymetazoline. The capacity of this suppressive effect is large and not inhibited by IBMX. These results suggest that there is a functional compartmentalization of cAMP within the hepatocyte or among hepatocytes.     

The role of adenylate cyclase in ischemic preconditioning in the rat heart: a cytochemical study

Using catalytic cytochemistry the AC activity was studied during ischemic preconditioning (IP) (5 min occlusion of LAD and 10 min reperfusion) followed by 30 min regional ischemia in isolated Langendorff-perfused rat heart. In controls the specific precipitate of AC reaction was found on the sarcolemma (SL) and the junctional sarcoplasmic reticulum (JSR) of cardiomyocytes. After prolonged ischemia the reaction product was absent, whereas IP followed by prolonged ischemia protected the AC activity on SL and JSR. IP-induced enhancement of AC activity in this model was accompanied by significant reduction of ischemia/reperfusion fibrillation. The results suggest involvement of AC system in mechanisms of IP.     

The size of adenylate cyclase and guanylate cyclase from the rat renal medulla

The size distribution of adenylate cyclase from the rate renal medulla solubilized with the nonionic detergents Triton X-100 and Lubrol PX was determined by gel filtration and by centrifugation in sucrose density gradients made up in H₂O or D₂O. The physical parameters of the predominant from in Triton X-100 are ²20,w, 5.9 S; Stokes radius, 62 A; partial specific volume (v ), 0.74 ml/g; mass, 159,000 daltons; f/f₀, 1.6; axial ratio (prolate ellipsoid), 11. For the minor form the values are : ²20,w, 3.0; Stokes radius, 28 A; mass, 38,000 daltons; f/f₀, 1.2. The corresponding values determined in Lubrol PX are similar. The value of v for the enzyme indicates that it binds less than 0.2 mg detergent/mg protein. Since interactions with detergents probably substitute for interactions with lipids and hydrophobic amino acid side chains, these findings suggest that no more than 5% of the surface of adenylate cyclase is involved in hydrophobic interactions with other membrance components. Thus, most of the mass of the enzyme is not deeply embedded in the lipid bilayer of the plasma membrance. Similar studies have been performed on the soluble guanylate cyclase of the rate renal medulla. In the absence of detergent, the molecular properties of this enzyme are: ^s20,w, 6.3 S; Stokes radius, 54 A, v , 0.75 ml/g; mass, 154,000 daltons f/f₀, 1.4; axial ratio, 7. The addition of 0.1% Lubrol PX to this soluble enzyme increases its activity two- to fourfold and changes the physical properties to : ^s20,w, 5.5 S; Stokes radius, 62 A; v , 0.74 ml/g; mass, 148,000 daltons; f/f₀, 1.6; axial ratio, 11. These results show that Lubrol PX activates the enzyme by causing a conformational change with unfolding on the polypeptide chain. Guanylate cyclase from the particulate cell fraction can be solubilized with Lubrol PX but has properties quite different from those of the enzyme in the soluble cell fraction. It is a heterogeneous aggregrate with ^s20,w, 10 S; Stokes radius, 65 A; mass about 300,000 daltons. The conditions which solubilize guanylate cyclase also solubilize adenylate cyclase and the two activities can be separated on the same sucrose gradient.     

Calcitonin-sensitive adenylate cyclase in rat renal tubular membranes.

1. Renal tubular membranes from rat kidneys were prepared, and adenylate cyclase activity was measured under basal conditions, after stimulation by NaF or salmon calcitonin. Apparent Km value of the enzyme for hormone-linked receptor was close to 1 x 10(-8) M. 2. The system was sensitive to temperature and pH. pH was found to act both on affinity for salmon calcitonin-linked receptor and maximum stimulation, suggesting an effect of pH on hormone-receptor binding and on a subsequent step. 3. KCl was without effect areas whereas CoCl and CaCl2 above 100 muM and MnCl2 above 1 muM inhibited F- -and salmon calcitonin-sensitive adenylate cyclase activities. The Ca2+ inhibition of the response reflected a fall in maximum stimulation and not a loss of affinity of salmon calcitonin-linked receptor for the enzyme. 4. The measurement of salmon calcitonin-sensitive adenylate cyclase activity as a function of ATP concentration showed that the hormone increases the maximum velocity of the adenylate cyclase. GTP, ITP and XTP at 200 muM did not modify basal, salmon calcitonin- and parathyroid hormone-sensitive adenylate cyclase activities. 5. Basal, salmon calcitonin- and F- -sensitive adenylate cyclase activities decreased at Mg2+ concentrations below 10 mM. High concentrations of Mg2+ (100 mM) led to an inhibition of the F- -stimulated enzyme. 6. Salmon calcitonin-linked receptor had a greater affinity for adenylate cyclase than human or porcine calcitonin-linked receptors. There was no additive effect of these three calcitonin peptides whereas parathyroid hormone added to salmon calcitonin increased adenylate cyclase activity, thus showing that both hormones bound to different membrane receptors. Human calcitonin fragments had no effect on adenylate cyclase activity. 7. Salmon calcitonin-stimulated adenylate cyclase activity decreased with the preincubation time. This was due to progressive degradation of the hormone and not to the rate of binding to membrane receptors.     

Parathyroid hormone stimulates adenylate cyclase in rat cerebral microvessels

We have studied the effect of parathyroid hormone (PTH) on adenylate cyclase of microvessels isolated from rat cerebral cortex. Native bovine (b) PTH-(1–84), the synthetic amino-terminal fragment bPTH-(1–34) and the synthetic analog [Nle⁸, Nle¹⁸, Tyr³⁴]-bPTH- (1–34) amide stimulated adenylate cyclase in a dose-dependent manner with apparent ED₅₀ values of 16 nM, 6.3 nM and 15 nM respectively. The stimulation by bPTH was greatly enhanced by guanosine triphosphate. The PTH antagonist, [Nle⁸, Nle¹⁸, Tyr³⁴]-bPTH-(3–34) amide inhibited the action of bPTH-(1–84) and bPTH-(1–34). In summary, PTH stimulated adenylate cyclase in rat cerebral microvessels in a very similar manner to its stimulation in the renal cortex.     

Comparison of the muscarinic-cholinergic and lysophosphatidate inhibition of fibroblast adenylate cyclase demonstrating desensitization to the cholinergic stimulus

Muscarinic stimulation of cultured fibroblasts decreases initial rates of cAMP accumulation in response to hormones 50–70%. This inhibitory effect of muscarinic stimulation on cAMP accumulation in intact cells was desensitized 65–75% by a 60 min pretreatment with the muscarinic agonist carbachol (10 μM), with a $\text{t}\text{1}\text{2}$ of 11 min. The carbachol pretreatment resulted in a diminished carbachol inhibition of adenylate cyclase in broken cell preparations. The phospholipid monooleylphosphatidate (MOPA) which also inhibited hormone-stimulated cAMP accumulation with a half maximal effect at 0.03 μM (as compared with 0.5 μM for carbachol), displayed many of the characteristics of muscarinic inhibition such as loss of activity with time of pretreatment. However, fibroblasts did not become desensitized to prolonged MOPA treatment; rather, it appeared that the MOPA was being inactivated. Also, the desensitization to carbachol did not prevent further inhibition by MOPA. The inhibitory effects of maximal doses of MOPA and carbachol in combination were no greater than the effect of carbachol alone, suggesting that they shared an intermediate in their inhibition of cAMP accumulation. These results are consistent with the hypothesis that muscarinic inhibition of adenylate cyclase is mediated by the formation of a phospholipid. However, the desensitization to the cholinergic stimulus does not appear to involve the intermediate, but rather a modification at the receptor level.     

Ultracytochemical localization of adenylate cyclase activity in rat thymocytes

Summary Ultrastructural localization of adenylate cyclase (AC) activity was investigated in suspensions of unfixed isolated rat thymocytes using a medium containing 0.6 mM 5-adenylylimidodiphosphate (AMP-PNP) as a substrate, 10 mM MgSO₄ as an activator, 5 mM theophylline as an inhibitor of 3,5-AMP-phosphodiesterase and 2 mM lead nitrate as a capturing agent. AC activity was demonstrated in plasma membrane, perinuclear space, endoplasmic reticulum, Golgi complex, centriole microtubules and mitochondria. AC was activated with 10^–4 M adrenalin in the presence of 5-guanylylimido-diphosphate (GMP-PNP) as well as with 10^–2 M NaF. In the cells incubated in a medium devoid of theophylline and containing 5-AMP instead of AMP-PNP, 5-nucleotidase activity was observed in the same cell structures as AC activity. Hydrolysis of 5-AMP in the nucleus was much stronger than that of AMP-PNP. 10 mM NaF markedly inhibited hydrolysis of 5-AMP in all cell structures. No staining was observed with 2 mM -glycerophosphate as a substrate. Incubation of unfixed thymocytes in media containing AMP-PNP, 5-AMP or p-nitrophenyl phosphate, but not -glycerophosphate, induced both in the nucleus and in the cytoplasm in some cells an appearance of a transitory reticular formation consisting of about 30 nm thick strands which could penetrate the nuclear envelope and plasma membrane and form connections with adjacent cells. The transitory reticular formation seems to belong to the cytoskeleton and to be involved in cell aggregation.