Louis Diamond

Relaxation of cat tracheobronchial and pulmonary arterial smooth muscle by vasoactive intestinal peptide: lack of influence by peptidase inhibitors

1 Vasoactive intestinal peptide (VIP) caused concentration‐dependent relaxation in precontracted segments of trachea, hilar bronchus, intrapulmonary bronchus and intrapulmonary artery (IPA) isolated from cat lungs. 2 VIP‐induced relaxation responses were abolished by preincubation of tissues with the proteolytic enzyme, α‐chymotrypsin (2 units ml−1). At the concentration employed, α‐chymotrypsin treatment did not adversely affect tissue viability as isoprenaline and bethanechol continued to relax airways and IPA, respectively. 3 Aprotinin prevented enzymatic degradation of VIP by α‐chymotrypsin as demonstrated by the ability of VIP to relax tissues incubated with both the peptidase inhibitor and α‐chymotrypsin. 4 A spectrum of peptidase inhibitors, including aprotinin, leupeptin, bestatin, bacitracin, β‐phenylpropionic acid and captopril, individually or in combination, did not augment the relaxant effects of VIP in isolated pulmonary tissues. 5 These results suggest that local enzymatic degradation may not be a primary route for inactivation of VIP in cat isolated airways and IPA. If VIP acts as a neurotransmitter in these tissues, a mechanism other than enzymatic proteolysis may be responsible for terminating its action.

Effect of α-chymotrypsin on the nonadrenergic noncholinergic inhibitory system in cat airways

Abstract Electrical field stimulation of 5-hydroxytryptamine contracted cat trachea and bronchi in the presence of cholinergic and adrenergic blockade caused relaxation by activating intrinsic nonadrenergic noncholinergic (NANC) inhibitory nerves. Pretreatment of the tissues with the proteolytic enzyme, α-chymotrypsin, did not affect NANC inhibitory responses. Relaxations induced by vasoactive intestinal peptide (VIP) were abolished by α-chymotrypsin. These results suggest that VIP or related peptides may not act as the NANC inhibitory trasmitter in cat airways. However, the possibility remains that peptides not susceptible to degradation by α-chymotrypsin may mediate these NANC inhibitory responses.

The effects of antagonists of vasoactive intestinal peptide on nonadrenergic noncholinergic inhibitory responses in feline airways

Relaxations of the feline intrapulmonary bronchus (IPB) induced by VIP or nonadrenergic noncholinergic (NANC) inhibitory nervous stimulation were unaffected by the VIP receptor antagonist [Ac-Tyr1,D-Phe2]-GRF (1-29) (30 microM). A second VIP antagonist, [pCl-D-Phe6,Leu17]-VIP (30 microM), also had no effect on NANC relaxation responses or IPB sensitivity to VIP. However, responses to three of the four highest VIP concentrations were inhibited by this antagonist. These results indicate that [Ac-Tyr1,D-Phe2]-GRF (1-29) and [pCl-D-Phe6,Leu17]-VIP are not effective competitive antagonists of VIP receptors in feline airways and, hence, have but limited applicability in determining the role of VIP in mediating airway NANC inhibitory responses in this tissue.

Physiological factors affecting intestinal drug absorption.

Abstract An in situ technique for determining drug absorption rates from isolated segments of the gastrointestinal tracts of anesthetized animals has been described. In rats, the absorption half-lives for salicylic acid, barbital and haloperidol were found to be 8, 19 and 32 min respectively. When a fasting period exceeding 20–25 hr preceded the experiments, the absorption rates were found to decrease significantly and approximately in proportion to the fasting time. The influence of alterations in mesenteric blood flow on the absorption profile of sulfaethidole was investigated in anesthetized dogs. Reduction of intestinal blood flow to approximately 65%, 35% or 0% of initial values resulted in significant increases in absorption half-life. It is suggested that prolonged inanition may inhibit the intestinal drug absorption process by virtue of an induced diminution in intestinal blood perfusion.

The effect of epithelium removal on non-adrenergic, non-cholinergic inhibitory responses in the isolated central airways of the cat and guinea pig.

Epithelium removal from the feline or the indomethacin-treated guinea pig trachea had no effect on tissue sensitivity or responsiveness to the contractile actions of pharmacological agonists or electrical field stimulation. In the feline hilar bronchus, epithelium removal had no effect on tissue sensitivity or responsiveness to acetylcholine or electrical field stimulation but increased bronchial sensitivity to serotonin without affecting responsiveness. Non-adrenergic non-cholinergic (NANC) relaxation responses elicited by electrical field stimulation in airway preparations from either species were unaffected by epithelium removal. These results suggest that the epithelium does not modulate contractile responses in the feline trachea but may modulate the actions of specific contractile agonists in the feline hilar bronchus. Further, NANC relaxation responses appear to occur independently of the airway epithelium.

Inhibition of porcine pancreatic elastase-induced emphysema by eglin-c.

Eglin-c, a compound that inhibits rat elastase but has little effect on porcine pancreatic elastase (PPE), was employed to examine the role of endogenous elastase in PPE-induced emphysema. Twenty-four female Long-Evans rats were divided into three groups: control (n = 8), PPE (n = 9), and PPE + eglin-c (n = 7). Eglin-c (9 mg/rat) was intratracheally instilled 3 days after PPE treatment, twice weekly, until 3 days before pulmonary function testing. Function tests and lung fixation for morphometric analysis were carried out 15-34 days after PPE treatment. Intratracheal instillation of PPE (400 IU/kg) produced significant increases in functional residual capacity, dynamic and quasi-static compliances, total lung capacity (TLC), and mean linear intercept (MLI), as well as a significant decrease in carbon monoxide diffusion coefficient. However, no significant alterations in quasi-static compliance, TLC, or MLI were found in animals treated with PPE and eglin-c. Three additional groups were used to examine the effects of intratracheal instillation of saline or eglin-c: control (n = 9), saline (n = 8), and eglin-c (n = 10). No significant change in any respiratory parameter was found in either the saline or the eglin-c group, indicating no detectable alteration in pulmonary function caused by either the intratracheal procedure or eglin-c. These data suggest that endogenous elastase is an important contributing factor in the development of PPE-induced emphysema in the rat.

Relaxant effects of vasoactive intestinal peptide and bethanechol in cat intrapulmonary artery

The relaxant actions of vasoactive intestinal peptide (VIP) and bethanechol were examined on ring segments of intrapulmonary artery (IPA) isolated from cat lung. On a molar basis, VIP was 75 times more potent than bethanechol; however, VIP was less efficacious than bethanechol in reversing phenylephrine induced tone. Responses to VIP were unaffected by pretreatment of the tissues with atropine, indomethacin or avian pancreatic polypeptide. These results suggest that VIP may participate in the regulation of pulmonary vascular smooth muscle tone through a potent relaxant action that occurs independent of muscarinic cholinergic receptor activation or liberation of prostaglandins.

Comparison of five methods of analyzing respiratory pressure-volume curves

Five methods of analyzing the deflation limb of respiratory pressure-volume (PV) curves obtained from seven groups of rats that had undergone various treatments were compared. The five methods utilized measurements of: y intercept and slope with simple exponential curve fitting; area under the curve; volumes at fixed pressures; shape constant, k, of the sigmoid curve described by Paiva et al. (Respir. Physiol. 23:317, 1975); and quasi-static compliance. The seven groups of rats were treated as follows: control (n = 10); high tar/nicotine cigarette smoke exposure (n = 10); low tar/nicotine cigarette smoke exposure (n = 9); intratracheal elastase (n = 10); intratracheal elastase plus sham smoke exposure (n = 10); intratracheal elastase plus high tar/nicotine cigarette smoke exposure (n = 9); and intratracheal elastase plus low tar/nicotine cigarette smoke exposure (n = 10). Elastase treatment caused a leftward and upward shift of the PV curve and this shift was augmented by exposure to either high tar/nicotine or low tar/nicotine cigarette smoke. Using Duncans multiple range test, we found that the y-intercept measurement of method 1, the area under the curve, volumes at fixed pressures, and quasi-static compliance methods were better able to differentiate PV curves between groups than were the slope measurement of method 1 and the shape constant measurement of method 4.

Augmentation of elastase-induced emphysema by cigarette smoke: effects of reducing tar and nicotine content

The effects of reducing the tar and nicotine concentration of cigarette smoke were examined in a rat model of smoke-augmented, porcine pancreatic elastase- (PPE-) induced, pulmonary emphysema. Sixty-eight female Long-Evans rats were divided approximately evenly into seven groups: control, PPE, PPE plus sham smoke, high-tar/nicotine cigarette smoke (2R1; 38.8 mg total particulate matter and 2.2 mg nicotine per cigarette), low-tar/nicotine cigarette smoke (1R4F; 10.8 mg total particulate matter and 0.8 mg nicotine per cigarette), PPE + 2R1, and PPE + 1R4F. Three days after intratracheal administration of PPE (400 IU/kg), animals in the smoke-treated groups were exposed to 8-10 puffs of cigarette smoke daily, 7 d/wk for 12 wk. Sham-treated animals received room air in place of cigarette smoke. At the conclusion of the exposures, pulmonary function tests were performed under general anesthesia. Cigarette-smoke exposure alone did not produce significant changes in pulmonary function. Elastase-treated groups demonstrated significant increases in total lung capacity, functional residual capacity, and dynamic and static compliance, as well as significant decreases in carbon monoxide (CO) diffusing capacity and CO diffusion coefficient. Morphometric measurements of mean linear intercept demonstrated a loss of alveolar fine structure with enlargement of distal airspaces in PPE-treated rats. Exposure to either 2R1 or 1R4F cigarette smoke significantly enhanced many of the emphysematous changes produced by PPE, but there were no significant differences between the effects of the two smokes. These data indicate that reducing the tar and nicotine concentration of cigarette smoke does not lessen its ability to augment PPE-induced pulmonary emphysema in the rat.

Morphologic and physiologic response of lungs to steroid and cigarette smoke: an animal model

The combined effects of cigarette smoke inhalation and hydrocortisone acetate (HCA) treatment induce prominent abnormalities in lungs of C57BL/6 male mice. These abnormalities include (1) a marked reduction of pulmonary macrophage population which is normally elevated by smoke inhalation, (2) an accumulation of surfactant and flocculent material in alveoli, (3) a decrease in alveolar space surrounded by normal septal tissue, and (4) an increase in hypertrophied alveolar parenchyma. Concomitant with altered lung morphology, lung volume and gas diffusing capacity were significantly compromised in animals subjected to smoke exposure and steroid treatment. It was found that smoke inhalation or HCA administration alone had no ill effects on the animals. The data presented indicate that manifestation of pathologic conditions resembling pulmonary fibrosis and pulmonary alveolar proteinosis is a result of cigarette smoke-drug interaction. The information reported provides a basis for an animal model which might be applicable to assessment of factors related to smoke inhalation and development of pulmonary disorders.