Demonstration of both beta 1- and beta 2-adrenoceptors mediating negative chronotropic effects on spontaneous activity in isolated bovine mesenteric lymphatics

Lymphatic Contractile Function: A Comprehensive Review of Drug Effects and Potential Clinical Application

BACKGROUND

The lymphatic system and the cardiovascular system work together to maintain body fluid homeostasis. Despite that, the lymphatic system has been relatively neglected as a potential drug target and a source of adverse effects from cardiovascular drugs. Like the heart, the lymphatic vessels undergo phasic contractions to promote lymph flow against a pressure gradient. Dysfunction or failure of the lymphatic pump results in fluid imbalance and tissue oedema. While this can due to drug effects, it is also a feature of breast cancer-associated lymphoedema, chronic venous insufficiency, congestive heart failure and acute systemic inflammation. There are currently no specific drug treatments for lymphatic pump dysfunction in clinical use despite the wealth of data from pre-clinical studies.

AIM

To identify (1) drugs with direct effects on lymphatic tonic and phasic contractions with potential for clinical application, and (2) drugs in current clinical use that have a positive or negative side effect on lymphatic function.

METHODS

We comprehensively reviewed all studies that tested the direct effect of a drug on the contractile function of lymphatic vessels.

RESULTS

Of the 208 drugs identified from 193 studies, about a quarter had only stimulatory effects on lymphatic tone, contraction frequency and/or contraction amplitude. Of FDA-approved drugs, there were 14 that increased lymphatic phasic contractile function. The most frequently used class of drug with inhibitory effects on lymphatic pump function were the calcium channels blockers.

CONCLUSION

This review highlights the opportunity for specific drug treatments of lymphatic dysfunction in various disease states and for avoiding adverse drug effects on lymphatic contractile function.

Electrical stimulation-induced alpha1- and alpha2-adrenoceptors-mediated contractions of isolated canine lymph nodes

The contractile effects of alpha-adrenoceptor agonists and field electrical stimulation were investigated pharmacologically in canine isolated tracheobronchial lymph nodes. Addition of noradrenaline (NA), phenylephrine (Phe) and UK14,304 caused dose-related contractions of the isolated lymph nodes. Pretreatment with prazosin (3 x 10(-9), 3 x 10(-8) and 3 x 10(-7) M) shifted the concentration-response curve for phenylephrine to the right, whereas yohimbine (3 x 10(-7) M) did not affect the contractile responses to phenylephrine. On the other hand, the concentration-response curve for UK 14,304 shifted to the right by treatment with yohimbine (3 x 10(-9), 3 x 10(-8) and 3 x 10(-7) M) but not by prazosin (3 x 10(-7) M). Field electrical stimulation (25 V, 0.7 ms, 16 Hz) produced contractile responses of the lymph nodes. The electrical stimulation-induced contractions were completely reduced by pretreatment with tetrodotoxin (TTX) (3 x 10(-7) M) or bretylium (10(-6) M). Furthermore, phentolamine (10(-8), 10(-7) and 10(-6) M), prazosin (3 x 10(-9) and 3 x 10(-8) M) and yohimbine (3 x 10(-8) and 3 x 10(-7) M) significantly reduced the electrical stimulation-induced contractions in the preparations. The present findings suggest that there are both alpha1- and alpha2-adrenoceptors located on the smooth muscle cells in canine tracheobronchial lymph nodes, and that the adrenoceptors-mediated excitatory mechanisms of adrenergic innervation exist in the lymph nodes.

Augmenting cardiac contractility hastens myocardial edema resolution after cardiopulmonary bypass and cardioplegic arrest

Although myocardial edema is associated with cardiopulmonary bypass (CPB) and cardioplegic arrest (CPA), interventions to expedite edema removal have not been investigated. The primary mechanism for the removal of excess interstitial fluid in the heart is myocardial lymphatic drainage, but lymphatic function can be impaired by decreased contractility because of edema. The purpose of this study was to determine whether enhancing cardiac contractility would increase myocardial lymphatic function and hasten edema resolution after CPB. Sixteen dogs were subjected to CPB and 1 h of hypothermic CPA. After weaning from CPB, 10 dogs received an intravenous dobutamine infusion and 6 dogs received no inotropic support. We determined myocardial lymph driving pressure from the major cardiac lymphatic, myocardial water content by using microgravimetry, and the peak rate of left ventricular pressure increase (dP/dmax) by using micromanometry. Measurements were taken at baseline, during CPA, and 60 min after CPB. Compared with controls, dobutamine-treated dogs had an increased dP/dmax (P < 0.05), which was associated with higher lymph driving pressures (P < 0.05), resulting in lower myocardial water gain 1 h after CPB (P < 0.05). We conclude that the resolution of myocardial edema after CPB was hastened by dobutamine. Organized ventricular contraction and myocardial contractility seem to be important determinants of myocardial lymphatic function and myocardial edema removal. These findings suggest that the administration of inotropic drugs after CPB may hasten cardiac recovery.

IMPLICATIONS

Myocardial edema, which develops during cardiopulmonary bypass and cardioplegic arrest, contributes to cardiac dysfunction after heart surgery. This study demonstrated that enhancement of cardiac contractility by the administration of dobutamine after cardiopulmonary bypass and cardioplegic arrest was associated with increased myocardial lymphatic function and hastened edema resolution in dogs.

Effects of beta-adrenergic blockade or stimulation on net rate of hydrothorax absorption

We determined in anesthetised rabbits the net rate of liquid absorption (NRLA) from Ringer or 1% albumin-Ringer hydrothoraces with the beta-blocker propranolol (or nadolol) or the beta-agonist terbutaline. The beta-blocker reduced NRLA by 38% in 2 ml Ringer hydrothoraces, and did not change it in 2 ml albumin-Ringer hydrothoraces; hence, with beta-blocker NRLA became similar in both kinds of hydrothorax (0.31 +/- 0.02 ml/h). Terbutaline decreased NRLA by 25% in 2 ml Ringer hydrothoraces, and increased it by 29% in 2 ml albumin-Ringer hydrothoraces; hence, with terbutaline NRLA became similar in both kinds of hydrothorax (0.40 +/- 0.02 ml/h), and 25% higher than with beta-blocker. Because beta-adrenoreceptor activity inhibits lymphatic smooth muscles and may increase Na+ transport in epithelia, these results suggest that: (1) pleural mesothelium is provided with beta-receptors, which increase Na+ transport and seem activated by protein dilution, (2) beta-receptors of the pleural lymphatics are essentially silent with and without protein dilution, (3) the lymphatic drainage produced by smooth muscle activity is smaller than the increase in solute-coupled liquid absorption caused by mesothelium beta-receptors.

Characterization of beta-adrenoceptor subtypes and indications for two cell populations in isolated bovine mesenteric lymphatic vessels

The pharmacological characterization of beta-adrenoceptor subtypes and the identification of two cell populations were investigated in isolated bovine mesenteric lymphatic vessels. The beta-adrenoceptor agonists isoprenaline, dobutamine and salbutamol concentration dependently decreased the amplitude and the frequency of spontaneous contractions and the amplitude of electrically induced contractions. The order of potency was isoprenaline greater than salbutamol greater than dobutamine. These effects were competitively antagonized by atenolol with pA2 values close to 7 with isoprenaline and dobutamine as agonists, and near 5.5 with salbutamol as the agonist. Noradrenaline concentration dependently reduced electrically induced contractions, an effect which was reversed to a slight enhancement after blockade of beta-adrenoceptors with propranolol (10(-6) M). These results confirmed the presence of postjunctional beta 1- and beta 2-adrenoceptor subtypes in lymphatic vessels and provide the first indication of the existence of two pharmacologically and functionally distinct cell populations, one of which exhibits pacemaker activity.