Summary
A number of catecholamine and non-catecholamine β-adrenoceptor agonists, including
the lipolytically selective compound BRL 37344, were compared for lipolytic activity
on human and rat adipocytes. On rat adipocytes, all compounds were full agonists,
BRL 37344 being the most potent. On human adipocytes, only the catecholamines were
full β-adrenoceptor agonists. The other compounds were partial agonists, with intrinsic
activities declining in the order fenoterol > salbutamol > clenbuterol > BRL 37344.
This was the case with FFA- as well as with glycerol-production. Addition of 20 μM
phentolamine did not enhance BRL 37344 activity. The isopreneline- and BRL 37344-induced
lipolysis on rat white adipocytes was stereoselectively antagonized by enantiomers
of alprenolol, with atypical low potencies and stereoselectivity. It was concluded
that (1) human and rat adipocyte β-adrenoceptors mediating lipolysis are not essentially
different, (2) partial agonism in human adipocytes is not explained by enhanced re-esterification
and (3) BRL 37344 selectively stimulates rat adipocyte lipolysis.
Key words
Lipolysis - β-Adrenoceptor Agonists - Human Adipocytes - Rat Adipocytes - Free Fatty
Acids - Glycerol
