The influence of route of administration on the acute cardiovascular effects of cocaine in conscious unrestrained pregnant rats.

The intravenous route of administration, accessed via a subcutaneous vascular access port, has been recently suggested as an animal model for studying the developmental effects of maternal cocaine abuse in the pregnant and/or group-housed rat. The present study (1) assessed the cardiovascular effects of intravenous (IV) cocaine, delivered via bolus injection, in chronically catheterized near-term pregnant rats, and (2) compared the IV cardiovascular responses to those following cocaine delivered via the commonly employed subcutaneous (SC) and intragastric (IG) routes of administration. Pregnant gestation day 15 (GD15) young adult female Sprague-Dawley rats (n = 21) were anesthetized and catheters surgically implanted into the carotid artery, jugular vein, fundus of the stomach, and a subcutaneous pouch. On GD17-19, heart rate (HR) and mean arterial pressure (MAP) were assessed, using a within-subjects design, prior and subsequent to IV (3 mg/kg), IG (60 mg/kg), and SC (40 mg/kg) cocaine. An interval of 6 h separated IV and IG cocaine administration and an interval of 18 h separated IG and SC cocaine administration. The peak responses of HR (23% downward arrow) and MAP (37% upward arrow) following IV cocaine were noted within 0.5 min. In contrast, the peak responses of HR (4% downward arrow, 6% downward arrow) and MAP (2% upward arrow, 15% downward arrow) after IG (23 min) or SC (26 min) cocaine, respectively, were significantly smaller and markedly delayed. No significant change in aortic blood flow velocity was detected following cocaine via any route of administration, although phasic flow velocities (PFV) were differentially sensitive to route of administration (PFV(dias) not PFV(sys)); IV cocaine increased (55% upward arrow) whereas IG or SC cocaine decreased approximately 35% downward arrow) PFV(dias). The pressor effects of an equimolar dose of IV cocaine methiodide (3.9 mg/kg) were indistinguishable from those of IV cocaine (38% upward arrow vs. 37% upward arrow), as were the effects on PFV(dias) (83% upward arrow vs. 55% upward arrow). The lack of an effect of cocaine methiodide on HR was consistent with the bradycardia effect of cocaine attributable to central mediation of the baroreflex. Finally, the pressor effects of IV cocaine paralleled the rapidly peaking arterial plasma levels of cocaine noted within 30 s after the initiation of drug injection. In sum, prominent effects of IV cocaine on maternal cardiovascular physiology are noted; as such, the recent reports of a lack of maternal/fetal toxicity following daily (3-6mg/kg) IV cocaine during GD8-21 are not due to use of an ineffective drug dose. It was equally clear that the SC and IG routes of exposure did not reproduce the cardiovascular component(s) of the expected physiological response to cocaine.

Heterogeneous cellular expression of creatine kinase isoenzyme during normal rat heart development.

The degree to which developmentally related alterations in cardiac creatine kinase (CK) activity reflect modification of CK isoenzyme gene expression remains uncertain. The present studies addressed this question by assessing multiple aspects of CK in rat heart during the perinatal to adult transition. In addition to whole tissue, isolated and purified muscle and nonmuscle cells were studied, as well as myofibrillar, mitochondrial, and cytosolic subcellular fractions. Whole homogenate CK enzyme specific activity nearly doubled during the weanling to adult developmental period. Muscle cell CK activity increased by a similar magnitude. Nonmuscle cell activity decreased. In the adult heart, both myofibrillar and mitochondrial CK activities were augmented versus the weanling heart. The cytoplasmic fraction activity held constant during development. Electrophoretic isoenzyme analyses of both weanling and adult cardiac muscle cells indicated the presence of mitochondrial CK and MM-CK isoforms. Weanling heart nonmuscle cells contained mitochondrial, MM, MB, and BB isoforms; however, BB isoform was not detected in the adult heart nonmuscle cells. Arrhenius plots provided information regarding heart muscle and nonmuscle cell alterations during development. CK activation energies were also determined for whole tissue, muscle/nonmuscle cells, myofibrils, mitochondria, and cytosol. Results demonstrate that heterogeneous muscle/nonmuscle cellular composition and differential myofibrillar/mitochondrial subcellular composition account for normal, developmentally related changes in heart CK enzyme activity. CK isoenzyme gene expression changes were not detected in cardiac muscle cells, and transition of CK-B to CK-M gene expression is limited to nonmuscle cells during normal, weanling to adult development in the rat heart.

Maternal hemodynamics and uteroplacental blood flow throughout gestation in conscious rats.

The present studies were conducted to develop experimental methods for obtaining cardiovascular measurements in conscious, pregnant rats. Methods were then used to establish key quantitative measurements of (a) placental and fetal development, (b) maternal hemodynamics and (c) uteroplacental blood flow throughout gestation. A progressive and significant enhancement in fetal weight occurs during the later one-third of gestation, commencing at day 15 of pregnancy. Fetal mass increases from 100 mg to 6,500 mg over this time period. Placental weight increases concurrently; however, over the last one-third of gestation, fetal growth and development outstrips placental augmentation such that each placental unit supports 10 fetal units near-term. As late gestation proceeds, a progressive reduction in mean arterial blood pressure is accompanied by enhancement in cardiac output. Total peripheral resistance is significantly reduced. Starting at day 15 of gestation, progressive and significant enhancement in blood flow to uterine tissue occurs. Moreover, significantly greater percentage of cardiac output is directed toward uterine tissue, especially near term. Percentage uterine blood flow directed to placenta is less than 10% at day 15 gestation, but placental perfusion is preferentially enhanced as late gestation continues. Near-term, 90% of uterine blood flow perfuses the placenta. Blood flows to nonreproductive visceral organs (kidney, liver, gut and spleen) and skeletal muscles (gastrocnemius, plantaris, tibialis anterior and soleus) are unaltered by pregnancy and gestation. Therefore, late gestational rat fetal development is supported by cardiovascular adaptations, including specific regional control mechanisms, qualitatively similar to those occurring during human gestation.

Aortic peak flow velocity as an index of myocardial contractility in the conscious rat.

The present studies were conducted in conscious, instrumented rats to evaluate measurements of aortic peak flow velocity (PFV) as an index of myocardial contractility. Because our previous studies had characterized/verified procedures to determine pressure-derived indices of contractile function in the anesthetized, ventilated, open-chest rat, we first correlated PFV with (a) maximum rate of left ventricular pressure development (max +dP/dt) and (b) a contractility index derived by dividing max +dP/dt by left ventricular pressure at max +dP/dt [(dP/dt)/P] in anesthetized rats (n = 5). The positive inotropic agent, isoproterenol, given by bolus intravenous injection (0.2 microgram), significantly and concurrently increased dP/dt, (dP/dt)/P, and PFV. The negative inotropic agent, propranolol, given by bolus intravenous injection (2 mg/kg), significantly and concurrently attenuated all of the above measurements. When control, isoproterenol, and propranolol responses were used to calculate multivariate correlation coefficients among dP/dt, (dP/dt)/P, and PFV, r values ranged from 0.74 (PFV vs. dP/dt) to 0.84 (dP/dt vs. (dP/dt)/P) to 0.91 (PFV vs. (dP/dt)/P). A separate group of rats (n = 4) was surgically implanted with ascending aortic blood flow sensors, carotid artery and jugular vein catheters. Intravenous isoproterenol (0.2 microgram, bolus) elicited increased cardiac (heart rate and cardiac output) and decreased peripheral vascular resistance (mean arterial blood pressure) beta-adrenergic receptor agonist effects. Propranolol (2 mg/kg, i.v. bolus) produced hemodynamic effects consistent with cardiovascular beta-adrenergic receptor blockade. Isoproterenol and propranolol had directionally appropriate, and significant effects on PFV in the conscious rat. When compared with PFV values under control conditions in the anesthetized rat, conscious rat values are approximately double those observed under anesthesia; however, the relative PFV responses to isoproterenol and propranolol were not affected. Therefore, the present studies provide evidence that aortic PFV can be utilized as an estimate of heart contractile performance, i.e., myocardial contractility, in the conscious, instrumented rat.

Cardiovascular responses to cigarette smoke exposure in restrained conscious rats.

The effect of exposure to cigarette smoke on cardiovascular function was examined in conscious, restrained Sprague-Dawley rats. Rats were exposed to 3, 6 and 9 puffs of either air or cigarette smoke during the "break in" period and to 10 puffs on the day of the experiment (day 4). HR, cardiac output and mean arterial pressure were recorded continuously throughout the experimental period. Rats exposed previously to cigarette smoke generated from either low-nicotine (0.16 mg/cig.) or high-nicotine (2.45 mg/cig.) cigarettes showed a dose-related decrease in HR in response to restraint stress. In addition, exposure to cigarette smoke produced a further decrease in HR and cardiac output and an increase in mean arterial pressure. This effect by cigarette smoke was dose-dependent (dependent on the cigarette nicotine content) and was antagonized by intra-arterial pretreatment with the nicotinic antagonists mecamylamine and hexamethonium and also with the ganglionic blocker chlorisondamine. Intra-arterial pretreatment with atropine methyl bromide blocked the bradycardia in response to both restraint stress and cigarette smoke. Furthermore, pretreatment with an arginine vasopressin antagonist, d(CH2)5Tyr(Me)arginine vasopressin, significantly attenuated the increase in mean arterial pressure and total peripheral resistance and the decrease in HR and cardiac output due to cigarette smoke. On the other hand, pretreatment with the opioid receptor antagonist naloxone had no effect on cardiovascular parameters in response parameters in response to cigarette smoke. These results implicate arginine vasopressin, in addition to the activation of both sympathetic and parasympathetic systems, in mediating cardiovascular responses to cigarette smoke.

Magnesium sulfate infusion during late gestation does not elicit a peripheral vascular steal and preserves placental perfusion.

Despite proven efficacy in interrupting uterine smooth muscle contraction for periods of 24-48 h, a recent clinical study concluded that the adrenergic beta-receptor agonist, ritodrine hydrochloride (Yutopar) had significant detrimental side effects. Our previous preclinical studies have shown that ritodrine reduces placental blood flow via a vascular steal phenomenon. Moreover, ovarian blood flow is reduced by approximately 40% by ritodrine treatment. Reduced ovarian blood flow during tocolytic treatment presented the possibility for a blood-flow-mediated decrease in progesterone secretion which would have negative effects on uterine quiescence. Pharmacological agents such as calcium channel blockers and magnesium sulfate have tocolytic potential. Magnesium sulfate infusion has a long clinical history of safety and efficacy; however, the possibility for latent detrimental hemodynamic and tissue/organ blood flow responses was unexamined. Therefore, the present studies examined hemodynamic and organ blood flow in near-term pregnant rats given intravenous MgSO4. Our results show that (a) peripheral vascular steal is not induced, and (b) placental perfusion is preserved during MgSO4 infusion. However, ovarian blood flow is significantly reduced and blood-flow mediated decrease in progesterone secretion requires consideration during implementation of tocolysis via MgSO4 infusion.

Enzymatic method for quantitating creatine kinase M and B isoenzyme composition in cardiac tissue: consideration for utilization in studies of developing and adult rat heart.

Creatine kinase (CK) is a cardiac enzyme of interest due to its involvement in both mitochondrial and contractile protein aspects of heart function. Studies on the structure, function, and developmental expression of myofibrillar CK led to the identification of specific isoenzymes whose synthesis can be mediated by changes in expression at two primary gene loci. Experimental interventions which alter gene expression and protein synthesis in other cardiac enzymes have been attempted to pinpoint underlying genetic and molecular CK control mechanisms. CK isoenzymes can be separated electrophoretically and then quantitated by densitometry; however, these methods are time consuming and require specialized instruments. Enzyme specific activity can be assessed spectrophotometrically, but this method, alone, does not provide isoenzyme quantitation. The present work establishes a rapid, simple spectrophotometric enzyme assay procedure based on relative thermal lability to quantitate tissue CK isoenzyme composition. Applicability to cardiac tissue having (a) heterogeneous muscle/nonmuscle cells and (b) heterogeneous subcellular fractions within a given cell population was evaluated. Results show that cardiac tissue from newborn, weanling, and adult rats undergoes dramatic and progressive augmentation of overall CK enzyme activity that may be mediated, at least in part, by altered CK gene expression. However, based on adult rat heart analyses, it is also apparent that cell makeup and fractional composition of subcellular constituents require consideration. The described activation energy method is simple, rapid, and reliable for initial screening for potential changes in CK isoenzyme expression which can then be verified by more detailed, albeit more complex, methodology involving mRNA and/or cDNA analyses.

Beta-adrenergic receptors, adenylate cyclase activation, and myofibril enzyme activity in hypothyroid rats.

A previous study in intact animals assessed cardiovascular alterations in surgically thyroidectomized rats. Hemodynamic challenge via isoproterenol infusion identified abnormal left ventricular relaxation. Challenge by aortic occlusion revealed a latent deficiency in left ventricular contractility which was not apparent during beta-agonist challenge. The present study utilized left ventricular cardiac tissue obtained from the identical control and thyroidectomized animals from which intact heart hemodynamic information had been obtained. Biochemical systems were selected for evaluation based on demonstrated hemodynamic alterations, i.e., beta-adrenergic receptor number/function and contractile protein enzyme properties. The number of beta-receptors on hypothyroid cardiac membranes was significantly decreased, but receptor agonist affinity was not influenced. Basal adenylate cyclase activity in cardiac membranes from control and thyroidectomized rats was nearly identical; however, isoproterenol activation was diminished in hypothyroid cardiac membrane, particularly at the higher levels of beta-agonist stimulation. Adenylate cyclase enzyme activation by forskolin was not influenced by thyroidectomy; however, activation by sodium fluoride was reduced approximately 30% when compared with preparations from control rats. Cardiac myofibrillar enzyme activity for adenosinetriphosphatase (ATPase) was significantly lower in thyroidectomized rats. Despite reduced ATPase activity, myofibrillar calcium sensitivity was unaltered. Myofibrillar creatine kinase enzyme activity was not influenced by thyroidectomy; therefore, compartmentalized ATP regeneration potential via creatine kinase was enhanced relative to substrate utilization via ATPase. Thus hemodynamically significant cardiac influences of hypothyroidism are mediated, at least in part, via 1) reduced beta-receptor number, 2) diminished catecholamine-induced activation of adenylate cyclase, and 3) reduced myofibrillar ATPase activity.

Enzymatic method for quantitating lactate dehydrogenase isoenzyme composition in cardiac tissue: utilization of the method to characterize newborn and adult rat heart.

Lactate dehydrogenase (LDH) is an enzyme of special interest due to its key position in anaerobic metabolic pathways. Work on the structure and developmental expression of LDH led to formulation of the isoenzyme concept as well as elucidation of the biological significance of isoenzymes. Tissue isoenzyme compositional changes are mediated by changes in pattern of gene expression for two primary LDH gene loci in vertebrates. Developmental shifts in LDH gene expression prompted other experimental interventions to alter gene expression schedule and enzyme synthesis in order to pinpoint underlying genetic and molecular control mechanisms. LDH isoenzymes in tissues can be separated by electrophoresis and then quantitated by scanning densitometry; however, these methods require specialized instruments. Enzyme specific activity can be assessed spectrophotometrically, but enzymatic activity determination alone does not provide quantitation of LDH isoenzyme(s). The present work was conducted to establish a spectrophotometric enzyme assay procedure based on differential substrate inhibition to quantitate tissue LDH isoenzymes. The procedure was then used to assess developmentally related alterations in LDH isoenzymes in cardiac tissue of newborn and young adult rats. Results show that heart tissue in 5-day old newborn rats possesses approximately equal proportions of muscle type (anaerobic) and cardiac type (aerobic) LDH isoforms. As normal development transpires, heart tissue LDH isoenzyme proportion shifts with substantial decrease in anaerobic form which is accompanied by marked augmentation in aerobic form.

Decreased ovarian blood flow may confound the tocolytic effect of ritodrine.

Pregnancies ending before 37 weeks gestation are the leading cause of infant morbidity and death. A recent study involving over 2,000 patients concluded that the beta-adrenergic agonist, ritodrine (Yutopar), the only tocolytic agent currently approved for clinical use, had no significant beneficial effect on perinatal mortality, the frequency of prolongation of pregnancy to term, or birth weight despite proven efficacy in suppressing uterine smooth muscle contraction for 24-48 h. Our previous studies in anesthetized, pregnant rats found that both isoproterenol and ritodrine decreased blood flow to the ovary, apparently via a 'vascular steal' phenomenon. Because decreased ovarian blood flow and blood flow-mediated decrease in progesterone secretion represents one potential mechanism to explain the long-term ineffectiveness of beta-agonist tocolysis, ovarian blood flow studies were conducted in conscious, pregnant rats. Our results indicate that, indeed, ritodrine infusion significantly decreases ovarian blood flow (40%) in the conscious, near-term pregnant rat.

Perinatal enhancement of cardiac myofibrillar creatine kinase activity without change in enzyme Km.

Myofibrillar creatine kinase (CK) serves as one microcompartment of the phosphorylcreatine shuttle by providing ATP as substrate for adenosinetriphosphatase (ATPase). During perinatal heart development, augmentations of myofibrillar ATPase and CK occur in concert with increased contractile performance. The maximal reaction velocity (Vmax) for CK doubles during development in both intact native myofibril and enzyme extracted from myofibril. The absence of alterations in ADP and creatine phosphate substrate Michaelis constants (Km), isoenzyme composition, or total number of -SH groups suggests active site function (Vmax) is influenced indirectly via a subunit domain effect on enzyme conformation.

Uteroplacental blood flow at rest and during exercise in late-gestation conscious rats.

The present studies were conducted to achieve three specific aims. First, techniques and procedures were developed to allow tissue and organ blood flow measurements by radioactive microsphere methodology in the conscious female rat. Second, technical aspects of the methodology were evaluated with emphasis on potential uteroplacental shunting of microspheres in the late-gestational period. Third, the above techniques and procedures were utilized to assess uteroplacental blood flow at rest and during exercise in conscious pregnant rats during the late stages of gestation, i.e., days 15, 19, and 22 of pregnancy. Results established the validity of tracer blood flow technical assumptions, and no significant increase in arteriovenous shunting of 15-microns microspheres either as pregnancy progressed or during superimposed exercise in near-term pregnant animals was detected. During the stages of pregnancy studied, cardiac output was enhanced approximately 20% near term. Marked and progressive increases in uterine blood flow were noted both in milliliters per minute and as percentage of cardiac output. Preferential placental perfusion during late-stage gestation was indicated by increased tissue flow (7 +/- 1, 84 +/- 12, 232 +/- 32 ml.min-1 x 100 g-1), increased percent cardiac output (1.7 +/- 0.1, 5.1 +/- 0.7, 11.0 +/- 1.7% cardiac output), and increased percent uterine blood flow (10 +/- 1, 59 +/- 3, 87 +/- 2% uterine flow) at days 15, 19, and 22 of gestation, respectively. Progressive maternal body weight increase during gestation enhanced exercise work intensity, as shown by heart rate and cardiac output at the end of 30 min of treadmill running at 8.5 m/min, 0% incline.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular alterations in the hypothyroid rat.

We conducted the present studies in intact animals to assess alterations in integrated cardiovascular function due to hypothyroidism. Rats were surgically thyroidectomized or sham operated. Most obvious among the alterations detected under resting conditions was the bradycardia present in hypothyroid animals. Cardiac output was significantly reduced by slower heart rate; however, mean arterial blood pressure and left ventricular +dP/dt were maintained. Total peripheral resistance was increased in hypothyroid animals. Functional responsiveness to hemodynamic challenges unmasked additional characteristics. Thyroidectomized animals had normal stroke index-left ventricular end diastolic pressure relationships in response to rapid volume infusion. Peak left ventricular +dP/dt response to brief aortic occlusion was attenuated in thyroidectomized animals. Hypothyroid rats failed to augment left ventricular -dP/dt in response to isoproterenol challenge. Moreover, isoproterenol failed to reduce total peripheral resistance in the hypothyroid rat. Therefore, the hemodynamic responses observed in the intact, hypothyroid animal are consistent with the presence of (a) decreased cardiac contractile protein ATPase, (b) reduced calcium uptake by cardiac sarcoplasmic reticulum and (c) altered vascular adrenergic receptors. Many cellular and subcellular defects are compensated by integrative mechanisms operating under resting conditions, while other defects are unmasked only when examined in the intact, functional cardiovascular system undergoing hemodynamic challenge.

Neural respiratory responses to cortically induced seizures in cats.

Seizure activity can lead to profound respiratory stimulation in spontaneously breathing animals with intact respiratory feedback mechanisms (Paydarfar et al., Am. J. Physiol. 260, R934, 1991). The present study was designed to test the hypothesis that peripheral respiratory feedback mechanisms are not important for the genesis of seizure-induced hyperpnea. Studies were performed in 16 anesthetized, vagotomized, glomectomized cats whose end-tidal PCO2 (PETCO2) was kept constant. Integrated phrenic nerve activity was used to represent respiration. Seizures were induced by injection of penicillin into the parietal cortex and electrocorticographic (ECoG) and biceps femoris nerve activities, arterial pressure, airway PCO2 and brain temperature were recorded continuously. Progressive seizure activity was associated with progressive increases of respiratory frequency and peak phrenic activity, despite constancy of PETCO2 and brain temperature. Patterns of entrainment were identified among ECoG spikes, biceps femoris nerve and phrenic nerve activities. Phrenic nerve activity became highly irregular during generalized ictal seizures and ceased to respond to changes of PETCO2. Acute intercollicular decerebration in all experiments resulted in normalization of respiratory rhythm even while ictal ECoG activity continued. We conclude that stimulation of breathing during seizures occurs in the absence of respiratory feedback mechanisms. The findings suggest that an important cause of the respiratory response is a feedforward mechanism, whereby activation of subcortical structures above medulla and pons results in stimulation of breathing.

Reproductive organ blood flow measured using radioactive microspheres in diestrous and estrous mice.

Blood flow is a primary mechanism controlling reproductive organ functions. In the present study, radioactive microsphere techniques were adapted to measure ovarian, uterine, and vaginal blood flow levels in C57BL mice. Anesthetized animals were tracheostomized and the left carotid artery was cannulated. The heart was exposed and 113Sn-labeled spheres (15 microns size, 2 microCi, 0.1 ml) were injected via the left ventricle. Reference sample was obtained by carotid artery blood "free flowing" into a tared microfuge tube for 1 min. The animal was killed, and selected tissues were excised for weighing and radioactivity measurement to determine flow. Absence of differences in flow levels (ml.min-1.g-1) to paired nonreproductive organs (adrenals and kidneys) validated the procedure. Blood flow levels were significantly higher in the ovaries, but not in the uterus and vagina of estrous mice vs. diestrous mice. Comparison of left vs. right ovaries suggested consistent blood flow distribution during diestrus. Ovarian blood flow level is enhanced during estrus and, in addition, is highly nonuniform regarding right-left flow distribution. Nonuniform ovarian blood flow distribution in estrous mice leads us to speculate that alternating right-left (i.e. nonuniform) ovulation predominates during each murine estrous cycle.

Cardiac myofibrillar creatine kinase Km is not influenced by contractile protein binding.

Subcellular microcompartmentation underlies the proposed phosphorylcreatine shuttle mechanism in mammalian cardiac tissue. In mitochondria, CK coupling to oxidative phosphorylation via adenine nucleotide translocase decreases the Km for ATP and suggests both a functional and physical integration. In the present studies, substrate Km of myofibrillar CK was unaltered when determined in the intact, native state or after removal from the myofibril. In contrast to mitochondria, close spatial proximity between cardiac myofibrillar CK and ATPase is sufficient to establish phosphorylcreatine shuttle microcompartmentation.

Anesthesia affects respiratory and sympathetic nerve activities differentially.

Phrenic and cervical sympathetic nerve responses to hypercapnia were examined before and after anesthesia in twelve midcollicularly decerebrated, vagotomized, glomectomized, paralyzed and ventilated cats. We measured responses of integrated phrenic and cervical sympathetic nerve activities to increases in end-tidal PCO2 (PETCO2) from apneic threshold to approximately 30 torr above threshold. All cats were studied first in the unanesthetized state. Six cats were then restudied after a quarter of a usual dose of chloralose/urethane (10 mg/kg and 62.5 mg/kg, respectively) and then after half the usual dose of chloralose/urethane (20 mg/kg and 125 mg/kg). The other six animals were restudied after quarter of a standard dose of pentobarbital (9 mg/kg), after half the standard dose (18 mg/kg) and then after the full (35 mg/kg) dose. Both anesthetic agents led to significant increases in apneic thresholds for both phrenic and sympathetic nerve activities. These agents also caused dose-dependent decreases in peak, tonic and respiratory-related sympathetic nerve activities. Peak (tidal) phrenic nerve activities, in comparison, were much less affected by the anesthetic agents. CO2 response curves showed that both of these anesthetic agents depressed, at any given level of PETCO2, respiratory-related sympathetic nerve responses more than the responses found in the phrenic nerve. We conclude that the relations between peak, tonic (i.e. between phasic bursts) and respiratory-related sympathetic nerve activities and phrenic nerve activity can be altered by anesthesia.

Comprehensive evaluation of cardiovascular function in the anesthetized rat.

The present report describes methods and procedures which have been developed and used in the intact, anesthetized rat for cardiovascular functional evaluation. Integrative hemodynamic mechanisms are ascertained under resting conditions by measuring arterial blood pressure, cardiac output and heart rate. Stroke volume and total peripheral resistance are derived from the above measurements. In addition, left ventricular pressure is determined by direct cardiac puncture. Derived rates of left ventricular pressure development (+dP/dt) and left ventricular pressure decline (-dP/dt) provide estimates of myocardial contractility and cardiac relaxation, respectively. Hemodynamic responses to isoproterenol infusion test the functional adequacy of the beta-adrenergic receptor, adenylate cyclase, cyclic AMP system. Ventricular function curves relating stroke volume and end-diastolic pressure during rapid volume infusion provide useful indices of cardiac pump performance in the intact heart. Peak left ventricular +dP/dt in response to brief aortic occlusion provides an index of cardiac contractile performance. Cardiac cellular/subcellular mechanisms relating (a) myofibrillar ATPase with heart contractility and (b) sarcoplasmic reticulum calcium handling properties with myocardial relaxation can be assessed. Thus, the methods and procedures described represent an experimental animal preparation which should prove useful for comprehensive evaluation of cardiovascular function.

Respiratory responses to focal and generalized seizures in cats.

We studied the effects on breathing of seizures induced by focal injection of penicillin G into the parietal cortex in 13 anesthetized cats. Electrocorticograms, ventilation, end-tidal PCO2, and intrapleural and arterial pressures were monitored; changes of these variables were related to the stages of motor seizure. The first respiratory responses, tachypnea and hyperpnea, usually occurred before any peripheral muscular contractions developed. Progression of the seizure was always accompanied by further tachypnea and hyperpnea. The hyperpnea associated with all stages of seizure activity resulted in hypocapnia, which was sustained even during prolonged tonic-clonic motor convulsions that caused a threefold increase of metabolic rate. The extreme tachypnea of tonic generalized convulsions led to increased end-expiratory lung volume because of dynamic hyperinflation associated with very short expiratory durations in the tonic phase. We suggest that the profound effects of seizures on respiration are by feedforward mechanisms from the cortical focus itself and from subcortical circuits, such as hypothalamus, that become involved during seizure propagation and generalization. Peripheral respiratory feedback mechanisms are not important for the genesis of seizure-induced hyperpnea.

Acetylcholinesterase molecular forms in muscle and non-muscle cells of rat heart.

Experiments were performed to determine the cellular associations of the molecular forms of acetylcholinesterase (AChE) in adult rat heart. For this purpose, a cardiac muscle and a non-muscle fraction were isolated from rat heart ventricles after perfusion with collagenase and hyaluronidase, extracts of these fractions were subjected to ultracentrifugation on linear density gradients of sucrose (5-20%), and fractions of these gradients were analyzed for AChE activity. The results show that only globular AChE molecular forms were present in isolated cardiac muscle cells. Globular AChE forms were also present in the non-muscle cells fraction but in different proportions. The proportions of globular AChE forms plus the high specific activity of choline acetyltransferase in the non-muscle cell fraction suggest that this fraction contains cholinergic nerve fragments. The results of this study also show that asymmetric AChE is released during the perfusion of heart with the digestive enzymes, which suggests that asymmetric AChE is bound to the extracellular matrix of heart.