Cardiovascular Response to Intravenous Administration of 5-Hydroxytryptamine after Type-2 Receptor Blockade, by Metrenperone, in Healthy Calves

in Veterinary Journal (1999), 157(1), 31-37

The cardiovascular response to 5-hydroxytryptamine (5-HT) challenge has been previously described in cattle. Abrupt bradycardia, followed by tachycardia, triphasic systemic blood pressure response, and ... [more ▼]

The cardiovascular response to 5-hydroxytryptamine (5-HT) challenge has been previously described in cattle. Abrupt bradycardia, followed by tachycardia, triphasic systemic blood pressure response, and pulmonary hypertension were the major changes elicited by 5-HT. The purpose of the present study was to determine whether the cardiovascular response to 5-HT in calves was attributable to 5-HT2 receptors. A specific 5-HT2 antagonist (metrenperone, 0.05 mg/kg) was administered intramuscular to six unsedated Friesian calves 30 min before the animals were given a 5-min intravenous 5-HT infusion. Mean systemic arterial (SAP), mean pulmonary arterial (PAP), pulmonary capillary wedge (PW) pressures were obtained by means of fluid-filled catheters, and cardiac output (CO) was measured by the thermodilution technique. Heart rate, stroke volume, systemic (SVR) and pulmonary (PVR) vascular resistances were calculated. Administration of 5-HT after metrenperone induced a short-lasting period of severe bradycardia followed by tachycardia and increased CO. The systemic blood pressure response was exclusively hypotensive and associated with a decrease in SVR. Conversely, PAP, PW, and PVR were not modified by 5-HT administration. The results establish that 5-HT induced systemic as well as pulmonary hypertension is mediated through the activation of type-2 serotonergic or alpha-adrenergic receptors, or both. In contrast, neither apnoea, bradycardia and hypotension, nor the positive chronotropic effect induced by 5-HT in cattle are mediated through such receptors. [less ▲]

Endocardite végétante dans l’espèce équine : revue de littérature à partir de 2 cas cliniques

in Annales de Médecine Vétérinaire (1998), 144

Les mycoplasmes respiratoires des bovins : II. Propriétés de virulence et vaccination

in Annales de Médecine Vétérinaire (1998), 142

Ventilatory Effects of the Single-Breath Co2 Test, Compared with Eructation, in Cattle

in American Journal of Veterinary Research (1997), 58(3), 310-6

OBJECTIVE: To assess the peripheral chemoreceptor-induced ventilatory response to single tidal-breath CO2 (SB CO2) tests, compared with eructations, in 2 breeds of calves. ANIMALS: 13 conscious unsedated ... [more ▼]

OBJECTIVE: To assess the peripheral chemoreceptor-induced ventilatory response to single tidal-breath CO2 (SB CO2) tests, compared with eructations, in 2 breeds of calves. ANIMALS: 13 conscious unsedated Holstein-Friesian and 8 Belgian White and Blue hypermuscled calves. PROCEDURE: An SB of +/- 50% CO2 in equal parts of O2 and N2 was inhaled. Ventilatory response was determined from the increase in ventilation (delta Ve) during the first 20 seconds after the test breath or eructation and from the difference in end-tidal PCO2 between the stimulus and preceding control breaths. RESULTS: Because no difference was found between the 2 breeds of calves, all data were pooled. The increase in Ve peaked during the fifth breath after the SB CO2 test on average, corresponding to a delay of 12.4 seconds. The SB CO2 responses ranged from 0.037 to 0.151 L/min.mm of Hg.m2, with a mean +/- SD of 0.082 +/- 0.032 L/min.mm of Hg.m2 for all calves. The SB CO2 tests, similar to eructations, modified the breathing pattern significantly and in the same direction, by principally shortening expiratory time and increasing mean inspiratory flow. After eructations, Ve peak increase was more important for lower difference in end-tidal PCO2 between the stimulus and preceding control breaths and took place more rapidly than after SB CO2 tests. Accordingly, eructation responses were more marked than SB CO2 responses and averaged 0.925 +/- 0.276 L/min.mm of Hg.m2. CONCLUSIONS AND CLINICAL RELEVANCE: In cattle, the pattern of breathing and ventilation under basal conditions is characterized by a cyclic variability coupled to eructation. [less ▲]

Parasympathetic component of 5-hydroxytryptamine-induced pulmonary dysfunctions in health calves

in American Journal of Veterinary Research (1996), 57(6), 896-901

Cardiovascular response to exogenous serotonin in healthy calves

in American Journal of Veterinary Research (1996), 57(5), 731-738

OBJECTIVE: To characterize the cardiovascular response to i.v. administration of serotonin (5-hydroxytryptamine [5-HT]) in calves. ANIMALS: 5 healthy unsedated Friesian calves. PROCEDURE: 41 5-HT ... [more ▼]

OBJECTIVE: To characterize the cardiovascular response to i.v. administration of serotonin (5-hydroxytryptamine [5-HT]) in calves. ANIMALS: 5 healthy unsedated Friesian calves. PROCEDURE: 41 5-HT administrations were performed: II slow infusions (duration, 5 minutes) and 30 bolus infusions (duration, 5 seconds). Cardiovascular function values were recorded before, during, and after the infusion. RESULTS: Slow infusion of 5HT first resulted in a brief period of severe bradycardia, then in sustained tachycardia with a concomitant increase in cardiac output. Systemic initial hypotension concomitant with bradycardia, then a pressor phase associated with an increase in systemic vascular resistance, and finally, a long-lasting hypotensive phase associated with decreased systemic vascular resistance. Pulmonary hypertension was associated with increased pulmonary vascular resistance, reflecting intense pulmonary vasoconstriction. Bolus infusion at increasing dosages resulted in dose-dependent bradycardia and systemic hypotension, followed by dose-dependent systemic hypertension. Unlike with slow infusion, neither the second tachycardiac nor the third systemic hypotensive phases were evident. CONCLUSIONS: 5-HT induces dose-dependent cardiovascular responses, including a reflex response followed by pulmonary and systemic vasoconstriction, in healthy calves. CLINICAL RELEVANCE: Determining the type of serotonergic receptors responsible for these responses may help to determine whether 5-HT is involved in the mechanisms underlying brisket disease in cattle. [less ▲]

The relation of ventilatory failure to pulmonary, respiratory muscle and central nervous system disturbances in calves with an experimentally produced pneumonia

in Journal of Comparative Pathology (1996), 115(3), 203-219

To explore the pathophysiology of respiratory failure in an experimental pneumonia, a Pasteurella haemolytica broth culture was injected intratracheally into 12 calves, which were then studied over a ... [more ▼]

To explore the pathophysiology of respiratory failure in an experimental pneumonia, a Pasteurella haemolytica broth culture was injected intratracheally into 12 calves, which were then studied over a period of 10 h. Measurements were made of inspired minute ventilation VE), ventilatory pattern [inspiratory time (TI), expiratory time (TE), respiratory rate (RR) and tidal volume (VT)], transdiaphragmatic pressure (Pdi), occlusion pressure at the airway opening 100 milliseconds after onset of inspiration (Pawo100ms), arterial blood gas tensions and pH and recorded diaphragmatic electromyogram (EMGdi) and rectal temperature (Tr). On and after the third hour after inoculation, the animals varied in respect of clinical signs, Tr, RR, VE, Pawo100ms/EMGdi, and arterial gases and pH. In benign cases, diminished alertness, laboured respiration and fall of arterial oxygen pressure (PaO2) worsened up to 7 h after inoculation, but then progressively improved, VE being maintained at approximately 150% baseline throughout the study (10 h). Neither arterial carbon dioxide pressure (PaCO2) nor pH was altered. Moderate cases resembled benign cases in respect of laboured respiration, VE, PaO2 and PaCO2; however, pH was at first maintained at preinoculation levels, but declined thereafter. In severe cases, the animals were drowsy between hours 3 and 7, and became comatose between hours 8 and 10; in contrast to both benign and moderate cases: (1) RR was reduced by hour 5, (2) there was no trend towards recovery of PaO2 and pH, (3) VE, Pdi, Pawo100ms and Pawo100ms/EMGdi were severely decreased, and (4) PaCO2 increased. These results suggest that pneumonia does not alter ventilatory neuromuscular pump function in calves, unless concomitant cardiovascular collapse occurs. It is not clear whether fatal ventilatory failure is caused mainly by deterioration in ventilatory muscle fibre processes or structures, altered central nervous system adjustment of ventilatory timing, or cardiovascular dysfunction. However, inspiratory pressures fall when excitation to the diaphragm is still growing, which suggests peripheral respiratory muscle fatigue. [less ▲]

Prophylactic activity of metrenperone-MDL 72222 association in calves given intravenous 3-methyl-indole

in Pflügers Archiv : European Journal of Physiology (1996), 431

Ruminal, cardiorespiratory and adrenocortical sequelae of Na2EDTA-induced hypocalcemia in calves

in Veterinary Research Communications (1996), 20

A study was undertaken to provide further information on the ruminal, cardiorespiratory and hypothalamo-pituitary-adrenocortical (HPAC) physiological sequelae of hypocalcaemia in dairy calves. The ... [more ▼]

A study was undertaken to provide further information on the ruminal, cardiorespiratory and hypothalamo-pituitary-adrenocortical (HPAC) physiological sequelae of hypocalcaemia in dairy calves. The functional picture observed in standing calves experiencing Na2EDTA-induced progressive hypocalcaemia showed a biphasic pattern. During the first phase (Ca2+ varying between 1.20 +/- 0.09 and 0.64 +/- 0.15 mmol/L, mean +/- SD), the animals became dull and lethargic, shifting their weight from one hind limb to the other, with cool extremities and hypersalivation. Their ventilation was slightly increased but their heart rate, thoracoabdominal pressure, pulmonary mechanics, haemoglobin and temperature remained constant. Conversely, their systemic arterial pressure (SAP) and the amplitude of their ruminal contractions (RCA) were severely decreased. During the second phase (Ca2+ < 0.64 +/- 0.15 mmol/L), there was restlessness, tachycardia, hypertension, polycythaemia and, finally, inability to stay upright. It is suggested that the diminished Ca2+ availability caused smooth-muscle and myocardial dysfunctions which could explain the RCA and SAP changes recorded during the first phase, whereas neural and/or humoral sympathetic discharge probably accounted for the reversal in SAP and heart rate when Ca2+ was decreased further. Serum cortisol increased regularly and remained significantly correlated with Ca2+ in each animal. Moreover, regression of delta cortisol/delta Ca2+ on delta Ca2+/delta Na2EDTA was significant (p < or = 0.001). It was concluded that mild asymptomatic hypocalcaemia severely impairs ruminal function, which will progressively worsen the Ca2+ deficit; that the inability to maintain posture in hypocalcaemia is not due to hypotension; and that the higher the HPAC response to hypocalcaemia, the higher the resistance to its effects. An asymptomatic periparturient cow with barely detectable ruminal activity may merit preventive calcium borogluconate therapy. Also, the physiological role of hypotension in explaining the clinical picture may be less important than other processes, such as neuromuscular failure. Finally, the present results imply a possible HPAC exhaustion in cows with periparturient paretic hypocalcaemia [less ▲]

De l'effet du transport sur la cortisolémie du cheval de sport (première thèse annexe)

Post doctoral thesis (1996)