Vasodilatory effect of tuberoinfundibular peptide (TIP39): requirement of receptor desensitization and its beneficial effect in the post-ischemic heart.

Tuberoinfundibular peptide of 39 residues (TIP39) is a member of the parathyroid hormone (PTH) family and a highly specific ligand of the PTH-receptor type 2 (PTH-2r). Recent studies have shown vasoactive properties of TIP39 in the kidney. This effect was stronger after desensitization of the parathyroid hormone-receptor type 1 (PTH-1r). The aims of our study were three-fold: (1) to investigate the influence of TIP39 on coronary resistance (CR), (2) to investigate a possible cross-talk between vascular PTH-receptors in the cardiovascular system, and (3) to investigate whether the endogenously released PTHrP during ischemia induces such a desensitizing effect. Experiments were performed on isolated rat hearts that were perfused with a constant pressure (Langendorff mode) and the coronary flow was determined. Under basal conditions, TIP39 showed no influences on CR. However, TIP39 reduced the CR by approximately 22% after pre-treatment of the hearts with a PTH-1r agonist. This TIP39 effect was abolished either by co-administration of a PTH-2r antagonist or by inhibition of nitric oxide (NO) formation. In an ischemia-reperfusion model endogenously released PTHrP desensitized the PTH-1r and pre-ischemic addition of TIP39 reduced post-ischemic CR by about 28%. Again, this effect was completely abolished in the presence of the PTH-2r antagonist or the PTH-1r-antagonist or by inhibition of NO formation. However, no effect was observed when TIP39 was washed-out prior to ischemia or if the treatment with TIP39 was restricted to the reperfusion. Furthermore, a pre-ischemic application of the NO-dependent vasorelaxant bradykinin provoked a similar effect on the post-ischemic CR than TIP39. In conclusion, a NO-dependent vasodilatory effect of TIP39 was demonstrated if the PTH-1r is desensitized by either exogenously applicated PTHrP peptides or endogenously released PTHrP.

N-terminal parathyroid hormone-related peptide hyperpolarizes endothelial cells and causes a reduction of the coronary resistance of the rat heart via endothelial hyperpolarization.

Parathyroid hormone-related peptide (PTHrP) is known to be a strong vasorelaxant peptide. The mechanisms by which PTHrP reduces the coronary resistance of the rat heart have not been worked out but seem to be independent of the classical PTH/PTHrP receptor-mediated, cAMP-dependent effect. In this study we hypothesized that PTHrP reduces the coronary resistance of the rat heart via endothelial cell hyperpolarization. Isolated microvascular endothelial cells from rat heart were incubated with PTHrP(1-36), and changes in the membrane potential were recorded via DiBAC fluorescence. Cells exposed to PTHrP showed a hyperpolarization of approximately 7mV. In the isolated Langendorff preparation, PTHrP-dependent vasodilatation of l-nitro-arginine-exposed hearts was abolished under depolarizing conditions (high potassium). Denudation of the endothelial cell layer significantly impaired the vasodilatory effect of PTHrP. In the presence of H89 (a cAMP/protein kinase A pathway antagonist) and indomethacin (a cyclooxygenase inhibitor), PTHrP dilated the vessels. In conclusion, PTHrP exerted a nitric oxide-independent vasodilatory effect that depends on endothelial cell hyperpolarization.

Cardiac-specific effects of parathyroid hormone-related peptide: modification by aging and hypertension.

OBJECTIVE: Parathyroid hormone-related peptide (PTHrP) improves heart function of post-ischemic and stunned myocardium and is released from the heart under ischemic conditions. Hypertrophic hearts from spontaneously hypertensive rats (SHR) develop a reduced ischemic tolerance, show reduced expression of PTHrP and develop paradoxical effects in regard to PTHrP. We hypothesized that PTHrP is causally involved in reduced ischemic tolerance of hypertrophied hearts. This hypothesis was tested by addition of a cardiac-specific PTHrP agonist or antagonist during ischemia and investigation of the functional recovery during the early phase of reperfusion. METHODS: Hearts from male normotensive adult (6 months) or old (12 months) Wistar and SHR rats were perfused at a constant flow for 20 min and then exposed for 30 or 15 min to global zero-flow ischemia followed by 30 min reperfusion. PTHrP agonist (PTHrP1-36) or antagonist (5Ile,23Trp,36Tyr-PTHrP1-36) (each 100 nmol/l) were added briefly before the onset of ischemia to ensure that they were present at the beginning of reperfusion. Heart function was determined by insertion of a balloon catheter into the left ventricle. Left ventricular developed pressure (LVDP), dP/dtmax, dP/dtmin, left ventricular end-diastolic pressure (LVeDP), heart rate (HR) and coronary resistance (CR) were recorded. RESULTS: Reduced post-ischemic recovery in old SHR was confirmed. Hearts from all four groups responded normally to exogenous PTHrP with a positive chronotropic effect under non-ischemic conditions. In hearts from adult normotensive rats, a beneficial effect of released endogenous PTHrP was confirmed. However, addition of the cardiac-specific PTHrP antagonist during ischemia significantly improved post-ischemic recovery in hearts from old normotensive rats and SHR. This beneficial effect of the antagonist was accompanied by a significant reduction in post-ischemic LVeDP and was more pronounced in adult SHR. This effect was also observed when the hearts were paced (4 Hz). Upon short-term ischemia (15 min), in the absence of ischemia-induced rigor contraction, the antagonist improved LVDP recovery in hearts from old normotensive rats. CONCLUSION: In summary, a protective effect of released endogenous PTHrP was confirmed for hearts from adult normotensive rats. This effect is converted into an opposite effect in hearts from SHR and old normotensive rats. Therefore, released endogenous PTHrP can contribute to reduced ischemic tolerance in hypertrophied hearts and during aging.

Sex-specific differences in ventricular expression and function of parathyroid hormone-related peptide.

OBJECTIVE: Parathyroid hormone-related peptide (PTHrP) expression is modulated by estrogen. It is expressed in coronary endothelial cells and involved in the endothelium-dependent regulation of coronary resistance and cardiac function. In the present study, we hypothesized that endogenously synthesized and released PTHrP contributes to sex-specific differences in the regulation of cardiac function. METHODS: The influence of sex on ventricular PTHrP expression in normotensive rats was determined via real-time PCR and immunoblot analysis. Sex-specific effects of exogenous PTHrP or endogenous released PTHrP were determined in vitro on isolated ventricular cardiomyocytes, Langendorff preparations on isolated hearts and in vivo using different agonistic or antagonistic PTHrP peptides. RESULTS: Ventricular expression of PTHrP was elevated in hearts from female rats compared to male counterparts. Addition of PTHrP(1-36) did not increase left ventricular function in hearts from either sex, but increased coronary flow in hearts from female rats significantly greater than in those from males. 5Ile-PTHrP(1-36), which was used to antagonize endogenously released PTHrP, reduced left ventricular function in females but not males in vitro and in vivo. Under conditions of increased endogenous PTHrP release, i.e. ischemia-reperfusion, antagonization of PTHrP significantly reduced post-ischemic recovery in hearts from females but not in those from males. CONCLUSIONS: Sex determines the ventricular expression of PTHrP mRNA and protein. The results indicate that PTHrP may improve cardiac function to a greater extent in women than in men following a brief period of ischemia.

Fever induction by localized subcutaneous inflammation in guinea pigs: the role of cytokines and prostaglandins.

In guinea pigs, dose-dependent febrile responses can be induced by injection of a high (100 micro g/kg) or low (10 micro g/kg) dose of bacterial lipopolysaccharide (LPS) into artificial subcutaneously implanted Teflon chambers. In this fever model, LPS does not enter the systemic circulation from the site of localized tissue inflammation in considerable amounts but causes a local induction of the proinflammatory cytokines tumor necrosis factor (TNF) and interleukin-6 (IL-6), which can be measured in lavage fluid collected from the chamber area. Only in response to the high LPS dose, small traces of TNF are measurable in blood plasma. A moderate increase of circulating IL-6 occurs in response to administration of both LPS doses. To investigate the putative roles of TNF and prostaglandins in this fever model, a neutralizing TNF binding protein (TNF-bp) or a nonselective inhibitor of cyclooxygenases (diclofenac) was injected along with the high or low dose of LPS into the subcutaneous chamber. In control groups, both doses of LPS were administered into the chamber along with the respective vehicles for the applied drugs. The fever response to the high LPS dose remained unimpaired by treatment with TNF-bp despite an effective neutralization of bioactive TNF in the inflamed tissue area. In response to the low LPS dose, there was an accelerated defervescence under the influence of TNF-bp. Blockade of prostaglandin formation with diclofenac completely abolished fever in response to both LPS doses. In conclusion, prostaglandins seem to be essential components for the manifestation of fever in this model.

Pharmacokinetics of pipamperone from three different tablet formulations.

Twenty-four (24) Caucasian male subjects completed a single-blind, randomised, three-treatment, three-period, cross-over study. In each treatment phase, subjects received a single dose of 144 mg pipamperone dihydrochloride (CAS 2448-68-2) (equivalent to 120 mg pipamperone; CAS 1893-33-0) as either the reference product (3 x 40 mg tablets), test product A (3 x 40 mg tablets) or test product B (1 x 120 mg tablet). Each consecutive dosing was separated by a washout period of 14 days. Following each dosing, venous blood samples were collected over a period of 120 h for the determination of plasma pipamperone concentrations by high-performance liquid chromatography. The most common drug related adverse events, ranging from mild to moderate in intensity, were bloodshot eyes, nasal congestion, dry mouth, hypotension and dizziness. The geometric mean Cmax of pipamperone for both the reference product and test product A was 266 ng/ml and for test product B 263 ng/ml. The geometric mean AUC0-infinity was 3107 ng.h/ml for the reference product, 3229 ng.h/ml for test product A and 3108 ng.h/ml for test product B. The two test products were shown to be bioequivalent to the reference product with respect to all pharmacokinetic variables investigated.

Influence of systemic treatment with cyclooxygenase inhibitors on lipopolysaccharide-induced fever and circulating levels of cytokines and cortisol in guinea-pigs.

Peripheral inflammatory stimuli result in the modification of a number of vital brain-controlled functions including the thermoregulatory set-point (induction of fever) and the activity of the hypothalamic-pituitary-adrenal (HPA) axis. We addressed the question of whether both of these components of the acute-phase response are induced by a common signal pathway. For this purpose we recorded body temperature (by remote radio-telemetry), HPA axis activity (circulating concentrations of cortisol by radio-immunoassay) and levels of the pro-inflammatory cytokines tumour necrosis factor and interleukin-6 (TNF, IL-6, using specific bioassays) in six groups of guinea-pigs. The animals received intra-arterial injections of either 10 microg/kg lipopolysaccharide (LPS) plus saline, 10 microg/kg LPS plus 5 mg/kg meloxicam (an inhibitor of the inducible form of cyclooxygenase), 10 microg/kg LPS plus 5 mg/kg diclofenac (a non-selective cyclooxygenase inhibitor), saline plus solvent, saline plus 5 mg/kg meloxicam or saline plus 5 mg/kg diclofenac. Injection of the cyclooxygenase inhibitors per se had no influence on the investigated parameters. Injection of LPS alone resulted in a biphasic fever, a more than fivefold increase in circulating cortisol and pronounced induction of TNF and IL-6. Treatment with the cyclooxygenase inhibitors either attenuated (meloxicam) or abolished (diclofenac) LPS-induced fever, but had no effect on the LPS-induced rise of plasma cortisol or IL-6. Circulating levels of TNF, in response to LPS, were enhanced by meloxicam and diclofenac, reflecting the negative feedback control exerted by prostaglandins on cytokine (specifically TNF) formation. These results provide the first evidence that the prostaglandin-dependent inflammatory pathway for fever induction is distinct from the pathway of HPA axis activation since fever, but not circulating cortisol, was attenuated by an inhibition of prostaglandin formation.