Female Sprague-Dawley rats were treated IM with 0, 2.5, 25, and 50 micrograms of clenbuterol HCl/kg of body weight/d for 21 days. In all treated rats, significant increase in body weight gain (P < 0.05) and improvement in feed conversion ratio (P < 0.05) were recorded. Hydrometra was observed in the uterus of treated rats, and histologically, it was possible to see dilatation of luminal glands and ovarian alterations. Clenbuterol treatment induced significant (P < 0.05) increase in uterine estrogen receptor concentration of rats treated with the 2 higher doses. Treatment apparently failed to enhance the rate of oxidative and conjugative biotransformations, except for glucuronidation of p-nitrophenol (P < 0.05). On the basis of the data obtained, we could affirm that high doses of clenbuterol affect the female reproductive system of rats inducing, almost in part, estrogen-like modifications, but probably by a different mechanism of action correlated to intense adrenergic stimulation.

In horses with noninduced, reversible airway obstruction (heaves), pulmonary function is improved after sedation with the alpha-adrenergic agonist xylazine. The mechanism of this effect is undetermined. Because the predominant excitatory innervation of equine airways is cholinergic, the influence of alpha 2-adrenergic receptor stimulation on the response of isolated distal airways to cholinergic stimulation was determined. Distal bronchial segments from 22 healthy horses were suspended in isolated organ baths where their mechanical responses to various stimuli could be studied. Each tissue was incubated with one of several concentrations of clonidine, clonidine vehicle, or clonidine plus tolazoline. Then, the contractile response of the tissues to either cumulative acetylcholine (ACh) addition or cumulative electrical field stimulation (EFS) was recorded. All contractile responses evoked by EFS were mediated through stimulation of cholinergic airway nerves. Clonidine had no effect on the contractile response of distal airway segments to exogenous ACh. However, clonidine (at concentrations > 10(-5) M) significantly (P < 0.05) diminished the contractile response of the distal airway segments to EFS. This inhibitory effect of clonidine was not observed in the presence of tolazoline. Similar results were observed when the less-selective alpha 2-adrenergic agonist xylazine was exposed to the isolated segments instead of clonidine. Because EFS-but not exogenous ACh-induced contractions were inhibited, alpha 2-adrenergic receptor stimulation apparently causes presynaptic inhibition of the cholinergic nerves innervating distal portions of the bronchi of horses.

The purpose of this study was to investigate the mechanism by which 5-hydroxytryptamine (5-HT) modifies respiratory function, specifically, hyperventilation, diffuse bronchoconstriction, and pulmonary arterial hypertension in cattle. We determined whether the IV response to 5-HT in calves was attributable to stimulation of 5-HT2 receptors. Six healthy unsedated young bull calves of the Friesian (n = 4) and of the Belgian White and Blue (n = 2) breeds were used. A specific 5-HT2 antagonist (metrenperone, 0.05 mg/kg of body weight) was administered IM 30 minutes before the cattle were given a 5-minute IV 5-HT infusion. Pulmonary function values were registered before, during, and after the 5-HT challenge infusion. Minute volume increased significantly, because of an increase in respiratory rate. Conversely, lung dynamic compliance, total pulmonary resistance, and pulmonary arterial pressure were not changed. We concluded that in cattle, 5-HT-induced ventilatory response is not mediated through activation of 5-HT2 receptors. However, the 5-HT2 receptors are involved in 5-HT-induced broncho- and pulmonary vasoconstriction.

Changes in lateral cecal arterial blood flow, mean internal carotid arterial pressure, and heart rate caused by nasogastric administration of fenoldopam (3, 6, and 9 mg/kg of body weight), a selective agonist of dopaminergic receptors, were recorded in 7 healthy horses. Cecal arterial blood flow was significantly increased within 30 minutes after administration of fenoldopam at all 3 dosages, with the peak increases from baseline (67.8 +/- 17.5 ml/min) being 125 +/- 28, 120 +/- 22, and 153 +/- 32 ml/min for 3, 6, and 9 mg/kg, respectively. Although carotid arterial pressure did not change significantly after administration of fenoldopam at the dosage of 3 mg/kg, administration of fenoldopam at the dosages of 6 and 9 mg/kg significantly reduced carotid arterial pressure from 113 +/- 10 to 88 +/- 3 and 81 +/- 5 mm of Hg, respectively. Intravenous infusion of metoclopramide, a dopaminergic receptor antagonist, at the rate of 0.125 mg/kg/h, blocked the effect of fenoldopam on cecal arterial blood flow and carotid arterial pressure. It was concluded that dopaminergic receptors mediate alterations in local blood flow and systemic pressure in horses.

Stimulatory effects of 6 zymosan preparations on luminol-dependent chemiluminescence (CL) responses of isolated bovine neutrophils were compared. Unopsonized zymosan particles and zymosan particles opsonized with bovine IgG1, IgG2, fresh serum, or serum from which zymosan-specific antibodies, but not complement, had been removed (C3- serum) induced strong CL responses, with nearly equal maximal peaks in the presence of extracellular Ca2+ and Mg2+, whereas the response to fetal bovine serumopsonized zymosan particles was markedly low. Removal of extracellular divalent cations almost completely blocked the CL reaction triggered by unopsonized, IgG1-opsonized, C3-opsonized, and fetal bovine serum-opsonized zymosan particles. By contrast, no change in the respiratory burst activity induced by serum-opsonized zymosan and only partial reduction in the response to IgG2-opsonized zymosan were seen under these conditions. Further experiments were performed with 4 zymosan preparations on neutrophils isolated from 2 calves with a genetic deficiency of CD11/CD18 membrane antigens. The unopsonized zymosan-induced CL reaction was absent in these cells. A reduced, but clear, response was observed with C3-opsonized zymosan. Unexpectedly, in the absence of extracellular Ca2+ and Mg2+ , serum-opsonized zymosan failed to generate the respiratory burst, whereas response to IgG2-opsonized zymosan was normal in the CDll/CD18-deficient neutrophils. These findings indicate that unopsonized zymosan may act in a divalent cation-dependent manner at the receptor for C3bi in bovine neutrophils, as it has been shown to do in the human system. In addition, it seems that IgG2-Fc receptors capable of signaling the respiratory burst in the absence of extracellular Ca2+ and Mg2+ exist on bovine neutrophils.

Bordetella avium is an important respiratory tract pathogen of turkeys. In common with other pathogenic bordetellae, B avium manifests a tissue tropism for cilia of the respiratory tract epithelium. To determine the molecular characteristics of the host cell receptors for B avium, we used hemagglutination and in vivo adherence assays. Carbohydrates, mucus, sialic acid-specific lectin, and other glycoconjugates were evaluated for their ability to competitively inhibit binding of B avium to host cells. The gangliosides, GD(1a) and GT(1b), completely inhibited hemagglutination, whereas N-acetylneuraminic acid (sialic acid) partially inhibited hemagglutination. Adherence to turkey tracheal mucosa in vivo was significantly (P < 0.01) inhibited by GD(1a) and GT(1b) gangliosides, N-acetylneuraminic acid, bovine sub-maxillary mucin, and horseshoe crab (Limulus polyphemus) lectin. Treatment of the tracheal mucosa with neuraminidase also inhibited adherence of B avium. We conclude that N-acetylneuraminic acid and the gangliosides, GD(1a) and GT(1b) may be important components of the tracheal mucosa receptor for B avium in turkeys.

Two types of sensory receptors were located in the equine foot, using anatomic techniques. Histologic examination of stained hoof sections revealed lamellated corpuscles in the hoof dermis, which had many of the morphologic characteristics of Pacinian corpuscles. These sensory receptors were restricted to the palmar (caudal) aspects of the solar dermis of the heel. A second type of receptor was detected by use of immunocytochemistry, indicating apparently naked nerve endings containing the neuropeptide calcitonin gene-related peptide-like immunoreactivity in skin, solar dermal tubules, and the digital cushion. This peptide is an example of a sensory neurotransmitter contained in dorsal root ganglion cells and is believed to exist only in unmyelinated sensory nerve fibers. These 2 morphologic structures may be used for detection of sensory stimuli, such as pressure (or vibratory senses) and pain, respectively, in horses during various locomotory gaits.