Significant Increase In Contractile Response Research Articles

Abnormal uterine artery remodelling in the stroke prone spontaneously hypertensive rat

IntroductionThe stroke prone spontaneously hypertensive rat (SHRSP) is an established model of human cardiovascular risk. We sought to characterise the uteroplacental vascular response to pregnancy in this model and determine whether this is affected by the pre-existing maternal hypertension. MethodsDoppler ultrasound and myography were utilised to assess uterine artery functional and structural changes pre-pregnancy and at gestational day 18 in SHRSP (untreated and nifedipine treated) and in the normotensive Wistar-Kyoto (WKY) rat. Maternal adaptations to pregnancy were also assessed along with histology and expression of genes involved in oxidative stress in the placenta. ResultsSHRSP uterine arteries had a pulsatile blood flow and were significantly smaller (70906 ± 3903 μm2 vs. 95656 ± 8524 μm2 cross-sectional area; p < 0.01), had a significant increase in contractile response (57.3 ± 10.5 kPa vs 27.7 ± 1.9 kPa; p < 0.01) and exhibited impaired endothelium-dependent vasorelaxation (58.0 ± 5.9% vs 13.9 ± 4.6%; p < 0.01) compared to WKY. Despite significant blood pressure lowering, nifedipine did not improve uterine artery remodelling, function or blood flow in SHRSP. Maternal plasma sFLT-1/PlGF ratio (5.3 ± 0.3 vs 4.6 ± 0.1; p < 0.01) and the urinary albumin/creatinine ratio (1.9 ± 0.2 vs 0.6 ± 0.1; p < 0.01) was increased in SHRSP vs WKY. The SHRSP placenta had a significant reduction in glycogen cell content and an increase in Hif1α, Sod1 and Vegf. DiscussionWe conclude that the SHRSP exhibits a number of promising characteristics as a model of spontaneous deficient uteroplacental remodelling that adversely affect pregnancy outcome, independent of pre-existing hypertension.

Modulation of airway responses by prostaglandins in young and fully grown rabbits

Maturational changes have been noted in neurally mediated contractile and relaxant responses in airways from New Zealand White rabbits. In this study, we focused on prostaglandins with bronchoprotective properties as potential modulators of airway tone in maturing rabbits. Tracheal rings from 1-, 2-, and 13-wk-old rabbits were assessed for neurally mediated contractile and relaxant responses produced by electrical field stimulation (EFS) of nerves in the presence and absence of the prostaglandin inhibitor, indomethacin (Indo). We also measured EFS-induced release of prostaglandin E(2) (PGE(2)) and the stable metabolite of prostacyclin, 6-keto-prostaglandin F(1alpha) (6-keto-PGF(1alpha)). In the presence of Indo, EFS produced significant increases in contractile responses in segments from 1- and 2-wk-old animals but not in segments from 13-wk adult rabbits. Tracheal rings from 1- and 2-wk-old animals precontracted with neurokinin A (NKA) relaxed 100% in response to EFS when Indo was not in the bath. In rings from 13-wk-old animals, relaxation was 40%. With Indo, relaxation was abolished in 1-wk-old animals and reduced to 30% in the 2- and 13-wk-old groups. Buffer from baths collected after EFS had significant increases in PGE(2) and 6-keto-PGF(1alpha) released from tissues from 1- vs. 2- and 13-wk-old animals. Dose response curves to PGE(2) using tissues precontracted to NKA showed significant increases in relaxant responses in 1- and 2- vs. 13-wk-old rabbits. In rabbit airways, this study demonstrates enhanced modulation of airway tone by PGE(2) and greater release of the bronchoprotective prostaglandins PGE(2) and prostacyclin early in life.

The effect of maternal cocaine exposure on neonatal rat cardiac function.

Fetal cocaine exposure has been associated with a variety of cardiovascular dysfunctions in humans. We treated pregnant rats with either saline or cocaine at 60 mg/kg by gastric lavage for the entire gestational period and for 14 days after parturition. We then performed high-frequency transthoracic echocardiography to determine whether cocaine exposure affected neonatal cardiac contractile function in vivo in 7- and 14-day-old neonatal rats. All studies were performed in the unsedated, conscious state. Heart rate (HR) and systolic function, expressed as fractional area of change at the midpapillary muscle level, were calculated from two-dimensional images. Resting HR was faster in the cocaine-exposed group at both ages, but baseline contractile function was not different between control (CTL) and cocaine-exposed (COC) neonatal rats. Dobutamine induced a significant increase in HR in all groups at only the largest dose tested (Day 7 CTL HR increased from 438 +/- 3 bpm to 462 +/- 10 bpm; Day 7 COC HR increased from 466 +/- 3 bpm to 493 +/- 7 bpm; Day 14 CTL HR increased from 443 +/- 4 bpm to 487 +/- 4 bpm; Day 14 COC HR increased from 477 +/- 4 bpm to 501 +/- 5 bpm). Dobutamine elicited a significant increase in contractile response at both Day 7 (from 76.6% +/- 0.6% to 81.5% +/- 0.7%) and Day 14 in CTL (from 78.2% +/- 0.7% to 81.9% +/- 0.7%), but not in COC, animals (from 76.7% +/- 0.8% to 78.9% +/- 0.8% at Day 7 and from 76.8% +/- 1.1% to 79.3% +/- 0.8% at Day 14). Epinephrine induced a significant increase in contractile response in CTL, but not in COC, rats at Day 7 and had no effect on fractional area of change at 14 days of age in either CTL or COC animals. Our results indicate that perinatal cocaine exposure does not modify resting contractile function but attenuates the contractile response to beta-adrenoceptor stimulation in the neonatal rat. These results suggest that perinatal cocaine exposure may lead to decreased responsiveness to inotropic drugs during the early neonatal period.

Effects of angiotensin II on nitric oxide generation in proliferating and quiescent rat coronary microvascular endothelial cells.

Nitric oxide (NO) and the mitogenic peptide angiotensin II (Ang II) have been implicated in endothelial cell growth. However, the putative relationship between these two opposing agents with respect to endothelial cell growth remains unknown. In this study, proliferating and confluent rat coronary microvascular endothelial cells (CMEC) were treated with different doses of Ang II, Ca2+ ionophore A23187, or valsartan (an Ang II type 1 (AT1) receptor inhibitor) alone or in combination for 24 h before measuring the nitrite levels as an index of NO generation. NO production and endothelial NO synthase (eNOS) mRNA/protein expression were found to be 3-fold greater in proliferating vs. quiescent CMEC. Treatments of CMEC with Ang II or Ca2+ ionophore A23187 equally increased NO production without altering the fold-difference in the basal release of NO from proliferating vs. confluent CMEC. Valsartan abolished NO production in CMEC treated with Ang II but not Ca2+ ionophore A23187. Treatments of endothelium-intact vascular rings with Ang II (1 nmol/l to 10 micromol/l) plus valsartan or PD-123319, an Ang II type 2 (AT2) receptor inhibitor, attenuated vascular responses to acetylcholine in an Ang II dose-dependent manner. In these rings, phenylephrine produced significant increases in contractile responses only at nmol/l concentrations of Ang II. In contrast, pharmacological and mechanical inactivation of endothelium enhanced contractile responses to phenylephrine at micromol/I concentrations of Ang II. These data demonstrate that Ang II stimulates NO production in CMEC in both an AT1- and an AT2 receptor-regulated manner, and that this stimulation of NO may be beneficial in counterbalancing the direct vasoconstrictor effect of Ang II on underlying smooth muscle cells.

UP-REGULATION OF BRADYKININ RESPONSE IN RAT AND HUMAN BLADDER SMOOTH MUSCLE

Responses to bradykinin were investigated in vitro in isolated control and hypertrophic smooth muscle strips from rat bladder. Bladder hypertrophy was induced by a 10-day period of partial urinary outflow obstruction. In addition, human bladder strips were also investigated. Bradykinin (1 nM. to 1 microM.) caused contractions in all tissues studied. In the freshly isolated rat bladder preparations bradykinin induced contractions were similar and of small amplitude in control and hypertrophic tissues. After a 4-hour equilibratory period contractile responses to bradykinin and the B1 specific bradykinin receptor agonist desArg9 bradykinin were slightly increased in the controls but there was approximately a 6-fold increase in the hypertrophic muscle strips. After 4 hours of equilibration the human bladder strips showed a smaller but still significant increase in contractile response to bradykinin. Indomethacin, a cyclooxygenase inhibitor, almost abolished the increased response, which suggests that prostanoids are involved in the up-regulated response. The protein synthesis inhibitor cycloheximide inhibited up-regulation by approximately 50% in hypertrophic and control muscle strips from rat bladder and normal muscle from human bladder. These results demonstrate that bradykinin receptor responses are present in rat and human detrusor muscle and they can be up-regulated in vitro. Experiments on hypertrophic rat bladder revealed that this process is enhanced in hypertrophy.

Modulation of Urinary Bladder Function by Sex Hormones in Streptozotocin-Diabetic Rats

The modulation of urinary bladder function by sex hormones was examined in castrated and sham-operated male and female streptozotocin-diabetic rats. Male and female diabetic rats weighed less than age-matched controls and had significantly greater serum glucose levels and bladder weights. Castration had no effect on bladder mass and did not alter the diabetes-induced changes in rat or bladder mass. Protein concentrations were significantly increased and collagen concentrations were significantly decreased in bladders from diabetic rats compared with nondiabetics. Sex or castration had no effects on protein or collagen concentration of bladders from nondiabetic and diabetic rats. There were no differences in water consumption and urine excretion between male and female nondiabetic rats, and no effects of castration were observed on micturition in nondiabetic rats. Ovariectomy followed by diabetes caused a significant increase in urine excretion compared with diabetes alone. Ovariectomized diabetic rats had increased mean and maximal micturition volumes when compared with other female rats. Orchiectomy had no effects on the expected increases in micturition associated with diabetes. Diabetes in male rats caused significant increases in contractile responses of bladder strips to field stimulation, carbachol, KC1 and high concentrations of ATP. In both nondiabetic and diabetic groups, orchiectomy had no effects on the contractile responses compared with sham operation. Similarly, in bladder strips from diabetic females, contractile responses to carbachol, KC1 and high concentrations of ATP were significantly increased compared with those of nondiabetics, and were unchanged by ovariectomy. However, ovariectomy in nondiabetic rats caused significant decreases in contractile responsiveness to nerve stimulation, effects which were only partially prevented by diabetes. The data suggest that there are few differences between male and female rats in their sensitivity to streptozotocin and the effects of diabetes on micturition, bladder collagen and protein concentration, and the responsiveness of bladder strips to contractile agents. The changes in bladder function observed after induction of diabetes do not appear to be related to changes in sex hormone levels. The major differences noted between males and females were the decreased responsiveness of bladders from nondiabetic ovariectomized female rats to field stimulation. In conjunction with previous data obtained in this laboratory, the study suggests that the responses to field stimulation are more sensitive to the effects of ovariectomy than are the responses to contractile agonists.

Hypercholesterolemia and atherosclerosis change vascular reactivity in rabbits by different mechanisms.

Vasomotor reactivity was assessed in vitro in arterial segments obtained from rabbits with different stages of atherosclerosis. Rabbits were fed a standard chow diet (controls) or a cholesterol-enriched diet to induce hypercholesterolemia and atherosclerosis. A third group received the hydroxymethylglutaryl coenzyme A reductase inhibitor, lovastatin, simultaneously with the cholesterol diet. Contractile responses of thoracic aortas to norepinephrine, serotonin, and potassium-rich solution, as well as endothelium-dependent dilations to acetylcholine, were compared after 2 and 4 months on the respective diet. Additionally, plasma cholesterol levels and the amount of plaques covering the intimal surface (as a percentage of the intimal surface) were determined; transmission electron microscopy of atherosclerotic arteries was also performed. After 2 months, the only difference was an enhancement of contractile responses to serotonin in the cholesterol-fed versus the control group. After 4 months on the diet, contractile responses to serotonin were further enhanced, and norepinephrine- and potassium-induced vasoconstrictions were now also significantly enhanced in cholesterol-fed animals versus controls. Endothelium-dependent vasodilations were simultaneously reduced in cholesterol-fed animals. These alterations were partly prevented in cholesterol-fed and lovastatin-treated animals. Suppression of nitric oxide synthesis in control aortas by NG-nitro-L-arginine did not reveal any significant increases in contractile responses. Contractile responses to serotonin were enhanced after 2 months on the diet but before the appearance of intimal plaques, whereas attenuation of endothelium-dependent dilations, as well as the further enhancement of contractile responses to serotonin and to other agonists, were closely correlated with the degree of intimal plaques after 4 months on the diet.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of Po 2, pH, and albumin on the in vitro contraction of vascular smooth muscle

A method by which gases can be added to a tissue bath containing proteins in solution is described and utilized in a study of the importance of O 2, CO 2 and albumin for the contraction of rings of rabbit pulmonary artery. In electrolyte solutions without protein, reduction of the oxygen tension from 700 to 150 mm Hg caused a shortening of the period during which contractions could be elicited by nerve specific electrical field stimulation before a significant decrease in the contractile response occurred. The addition of albumin (45 g/l) to the bath caused a significant increase in contractile response during the first hour and furthermore a prolongation of the period during which the following gradual decrease remained at an insignificant level. A reduction in oxygen tension in the albumin solution from 700 to 150 mm Hg caused a more abrupt and pronounced reduction in contractile response than the one seen in the protein free solution. The response increased when the pH in the saline solution was raised early during an experiment but not if the pH was raised later. Decreased responses were seen when the pH was reduced regardless of the length of the period prior to the pH change. It is emphasized that the method improves the possibilities for in vitro studies of the activity of protein bound drugs in the presence of dissolved proteins.