Inhibition of gastrointestinal mucosal glycoprotein synthesis by the beta-adrenergic blocking drug, practolol

beta-1 and beta-2, but not alpha-1 and alpha-2, adrenoceptor blockade delays rat cutaneous wound healing

The sympathetic nervous system plays an important role in wound healing, but its mechanism of action is poorly understood. The aim of this study was to investigate the effects of beta- and alpha-adrenoceptor blockade on cutaneous wound healing. Male rats were treated with propranolol (beta1- and beta2-antagonist), atenolol (beta1-antagonist), or phentolamine (alpha1- and alpha2-antagonist) dissolved in drinking water. A full-thickness excisional lesion was created and the wound area was measured. Fourteen days after wounding, lesions and adjacent skin were removed, formalin-fixed, and paraffin-embedded. Sections were stained with hematoxylin-eosin and toluidine blue, and immunostained for alpha-smooth muscle actin and proliferating cell nuclear antigen. Wound contraction was delayed in propranolol- and atenolol-treated animals but not in phentolamine-treated animals. Reepithelialization was decreased only in propranolol-treated animals. beta1- and beta2-adrenoceptor blockade delayed leukocyte migration, epidermal and connective tissue cell proliferation, myofibroblastic differentiation, and mast cell migration. The volume density of blood vessels was increased in the propranolol- and atenolol-treated animals compared with controls. The levels of matrix metalloproteases (MMP-2 and MMP-9) decreased in the propranolol- and atenolol-treated animals. alpha1- and alpha2-adrenoceptor blockade only affected leukocyte migration, epithelial and connective tissue cell proliferation, and pro-MMP-9 levels. In conclusion, beta-1 and beta-2, but not alpha-1 and alpha-2, adrenoceptor blockade delays cutaneous wound healing.

Beta-adrenoceptor blockade delays granulation tissue formation in polyurethane sponge implants

BACKGROUND

The role of adrenoceptors in granulation tissue formation is not well understood. The aim of this study was to investigate the effects of alpha- and beta-adrenoceptor blockade on granulation tissue development using polyurethane (PU) implants in the rat.

METHODS

Animals were treated orally with propranolol (beta1- and beta2-antagonist), atenolol (beta1-antagonist) or phentolamine (alpha1- and alpha2-antagonist) until euthanasia. The control group received only water. All animals received subcutaneous implants of PU sponges. After 14 days, implants were collected, formalin-fixed and paraffin-embedded. Sections were stained with hematoxylin and eosin and Sirius red and immunostained for CD68 and alpha-smooth muscle actin.

RESULTS

The number of inflammatory cells and the volume density of myofibroblasts and blood vessels were lower in the control group than in the propranolol- and atenolol-treated groups. The collagen fiber score was greater in the control group than in the propranolol- and atenolol-treated groups. The inflammatory infiltrate, collagen fiber score, blood vessel density or myofibroblast differentiation was not affected by phentolamine. The percentage of fibrovascular invasion was greater in the antagonist-treated groups than in the control group.

CONCLUSIONS

Blockade of beta1- and beta2-adrenoceptors, but not alpha-adrenoceptors, impairs granulation tissue development in PU implants due to interference with the inflammatory response.

Practolol inhibits human skin fibroblast cell mat hydroxyproline accumulation

Despite being poorly absorbed practolol (N-4-2-hydroxy-3-(1-methyl-ethyl)-amino propoxy phenyl acetamine) inhibited the accumulation of cell mat hydroxyproline, a measure of collagen synthesis, by human skin fibroblasts (DT2PH) in vitro, (ID50 0.8 X 10(-3) M). The degree of inhibition was dependent on the concentration of practolol used and the incubation time. Neither preinitiation of collagen synthesis nor omitting ascorbic acid from the incubation medium modified this inhibitory action. In contrast, in vitro generated metabolites of practol, using normal and aroclor induced hamster liver preparation, and structural analogues of practolol had no effect on cell mat hydroxyproline levels. Related compounds, propranolol, (1-(isopropylamino)-3(1-naphthyl-oxy)2-propranolol), and paracetamol, (N-(4-hydroxyphenyl)acetamide), both inhibited hydroxyproline levels. Fibroblasts derived from uninvolved skin of a psoriasis patient (PS1) were several fold more sensitive to practolol and propranolol than cells derived from normal skin but showed little change in sensitivity towards paracetamol.

The Effect of Practolol, In Vitro Generated Metabolites of Practolol and Chemical Analogues on the Rate of Growth of Human Skin Fibroblasts

The rate of growth of normal human skin fibroblasts was inhibited in a dose related, reversible, fashion by practolol (N-4-(2-hydroxy)-3 (1-methyl)-aminopropoxyphenylacetamine) (ID50 1.35 ± 0.14 x 10-3M), propranolol (1-(isopropylamino)-3(1-naphthyl-oxy)-2-propranolol) (ID50 0.145 ± 0.02 x 10-3M) and paracetamol (N-(4-hydroxyphenyl) acetamide) (ID50 0.85 ± 0.2 x 10-3M). Skin fibroblasts isolated from a psoriasis patient were more sensitive towards practolol (ID50 0.48 ± 0.14 x 10-3M) and propranolol (ID50 0.032 ± 0.002 x 10-3M), but less sensitive towards paracetamol (ID50 1.3 ± 0.07 x 10-3M). In vitro generated metabolites of practolol, using normal or Arochlor 1254-pretreated hamster liver preparations, and structural analogues of practolol had no effect upon the growth of either cell type.

Effect of some beta-adrenergic blocking agents on tissue guanylate cyclase and cyclic nucleotides in the rat

Pretreatment of rats with the beta-adrenergic blocking agents, atenolol, practolol, pronethalol and propranolol, at a dosage of 150 mg/kg/day for 5 days, produced marked increases in guanylate cyclase activity in the liver, gastric and intestinal mucosae, but with concomitant decreases in cyclic GMP levels. The ratios of cAMP/cGMP in each of the tissues were not changed significantly from control values after pretreatment with these drugs. These observations indicate that any oncogenicity seen with beta-blocking agents is not due to the common pharmacological action of beta-adrenoreceptor blockade.

Studies on the possible mutagenicity of beta-adrenergic blocker drugs

The mutagenic potential of nine beta-adrenergic blocking agents was investigated in the Ames and micronucleus tests. None of the drugs studied showed any mutagenic response in the Ames test, either in the presence or in the absence of an activation system. At the highest concentration oxprenolol and propranolol exhibited a bactericidal effect. In the micronucleus test the same drugs showed a weak, but statistically non-significant response, but only at the highest doses. It is concluded that there is no overt mutagenic or carcinogenic potential associated with beta-adrenergic blocking drug activity.