In vitro characterization of tripitramine, a polymethylene tetraamine displaying high selectivity and affinity for muscarinic M₂ receptors

Abstract

1 The antimuscarinic effects of tripitramine were investigated in vitro in isolated driven left (force) and spontaneously beating right (force and rate) atria as well as in the ileum of guinea-pig and rat and in the trachea and lung strip of guinea-pig and compared with the effects of methoctramine. 2 Tripitramine was a potent competitive antagonist of muscarinic M2 receptors in right and left atria. The pA2 values ranged from 9.14 to 9.85. However, in the guinea-pig and rat left atria but not in guinea-pig right atria, tripitramine at lower concentrations (3-10 nM) produced a less than proportional displacement to the right of agonist-induced responses owing to the presence of a possible saturable removal process. 3 Tripitramine was about three orders of magnitude less potent in ileal and tracheal than in atrial preparations (pA2 values ranging from 6.34 to 6.81) which makes it more potent and more selective than methoctramine. 4 Another intriguing finding was the observation that the pA2 value of 7.91 observed for tripitramine in guinea-pig lung does not correlate with that found at both muscarinic M2 and M3 receptor subtypes, which clearly indicates that the contraction of guinea-pig lung strip is not mediated by these muscarinic receptor subtypes. 5 A combination of tripitramine with atropine resulted in addition of the dose-ratios for left atria as required for two antagonists interacting competitively with the same receptor site, whereas the same combination gave a supra-additive antagonism on guinea-pig ileum which suggests that tripitramine interacts with a second interdependent site. 6 Tripitramine was more specific than methoctramine since, in addition to muscarinic receptors, it inhibited only frog rectus abdominis muscular (pICm value of 6.14) and rat duodenum neuronal (pIC5m value of 4.87) nicotinic receptors among receptor systems investigated, namely oa-, M2-, and Pladrenoceptors, Hl-and H2-histamine receptors, and muscular and neuronal nicotinic receptors.

Characterization of the muscarinic receptor in isolated uterus of sham operated and ovariectomized rats

“…Saturation experiments were conducted with eight concentrations of radioligand (0.04–5 n M ) and most competition displacement curves were generated with six concentrations of antagonists. To define M 2 and M 3 receptor proportions, 24 concentrations of tripitramine, a muscarinic antagonist with a marked degree of selectivity for M 2 over M 3 receptors ( Chiarini et al ., 1995 ; Roffel et al ., 1997 ), were used. Incubations were carried out to equilibrium (60 min at room temperature).…”

Selective changes in the <i>α</i>-adrenoceptor-mediated contraction in the senescent rat urinary bladder

“…In human detrusor muscle, M2 receptors existed three times more than M3 receptors according to the immunoprecipitation study [13]. The receptor binding assay also indicated that the percentages of M2 and M3 receptors were 60% -80% and 20% -40%, respectively [14,15]. Braverman et al reported that M2 muscarinic receptor contributed to rat urinay bladder contraction [16].…”

Polymethylene tetraamine backbone as template for the development of biologically active polyamines

“…However, in the guinea pig and rat left atria, but not in guinea pig right atria, tripitramine at lower concentrations (3-10 nM) produced a less than proportional displacement to the right of agonist-induced responses owing to the presence of a possible saturable removal process. 44 Tripitramine was about three orders of magnitude less potent in ileal and tracheal than in atrial preparations (pA 2 values ranging from 6.34 to 6.81) which makes it more potent and more selective than methoctramine. Furthermore, tripitramine was more specific than methoctramine because, in addition to muscarinic receptors, it inhibited only frog rectus abdominis muscular (pIC 50 , 6.14) and rat duodenum neuronal (pIC 50 , 4.87) nicotinic receptors among the set of receptor systems investigated, namely a 1 -, a 2 -, and b 1 -adrenoceptors, H 1 -, and H 2 -histamine receptors, and muscular and neuronal nicotinic receptors.…”

“…Furthermore, tripitramine was more specific than methoctramine because, in addition to muscarinic receptors, it inhibited only frog rectus abdominis muscular (pIC 50 , 6.14) and rat duodenum neuronal (pIC 50 , 4.87) nicotinic receptors among the set of receptor systems investigated, namely a 1 -, a 2 -, and b 1 -adrenoceptors, H 1 -, and H 2 -histamine receptors, and muscular and neuronal nicotinic receptors. 44 The antimuscarinic effects of tripitramine were assessed also in in vivo preparations, namely, anaesthetized and pithed rats. Tripitramine (0.0202 mmol/kg i.v.)…”