Evidence of functional <i>α</i>2-adrenergic receptors in adult-rat adipocytes by using the agonist UK 14304

Rebourcet, Marie-Christine; Carpéné, Christian; Lavau, M

doi:10.1042/bj2520679

Cited by 15 publications

(3 citation statements)

References 23 publications

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“…Recently, the presence of alpha2-adrenergic re¬ ceptors in male adult Wistar and Zucker rats was demonstrated (31). In the present report, a clear response was seen after stimulation by UK 14,304 (alpha2-adrenoceptors agonist), confirming these findings.…”

Section: Discussionsupporting

confidence: 91%

Testosterone treatment of ovariectomized rats: Effects on lipolysis regulation in adipocytes

Pergola

Holmäng

Svedberg

et al. 1990

Acta Endocrinologica

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The effects of testosterone treatment (2 mg every 14 days, for three months) on adipocyte lipolysis of intact (250-300 g body weight) and ovariectomized female rats were studied. Testosterone treatment of intact rats had no effect. Ovariectomy was followed by an increase in fat cell size and a decrease of lipolysis stimulated by isoproterenol, norepinephrine, epinephrine, forskolin, cAMP and isobutylmethylxantine. The number of \ g=b\ -adrenergic receptors was reduced. There was, however, no change in the antilipolytic effects of UK 14,304 (alpha2-adrenergic agonist), nicotinic acid, N -phenylisopropyladenosine or insulin. Testosterone treatment of ovariectomized rats restored the number of \g=b\-adrenoceptors and lipolysis stimulated by cAMP and isobutylmethylxantine, but not lipolysis stimulated by catecholamines and forskolin, suggesting a remaining defect in the catalytic unit of adenylate cyclase. These results indicate that ovariectomy is followed by a profound derangement of the lipolytic pathway at several levels, from \g=b\-adrenoceptors number to the triglyceride lipase activity. This is partially restored by treatment with testosterone, which, however, has no effect on intact female rats. This study emphasizes the importance of ovarian integrity for the lipolytic regulation and the inability of testosterone to replace ovarian function in this regard or to affect lipolysis in intact female rats.Sex steroid hormones influence adipose tissue me¬ tabolism and body fat mass through activation of specific intracellular receptors in adipocytes (1-4). Several studies have investigated the separate or combined effects of estrogen and progesterone on lipoprotein lipase activity (5-13), but only few reports have focused on the effects of these hor¬ mones on lipolysis. In female rats, estrogen treat¬ ment increases the lipolytic responsiveness to catecholamines and progesterone has no effect on the glycerol release (13-15); in male adipose precursor cells, testosterone enhances the lipolytic capacity of these cells by increasing the apparent number of ß-adrenoceptors and the activity of adenylate cyclase (3).It is now well established that accumulation of intra-abdominal fat in humans is closely associated with higher cardiovascular risk and disturbances in carbohydrate and lipid metabolism (16)(17)(18)(19); more¬ over, premenopausal women with abdominal obe¬ sity are characterized by increased androgenic ac¬ tivity (20-21) and more lipolytic abdominal adi¬ pocytes than women with gluteal-femoral obesity (22). Thus, androgens seem to be involved in these effects.Since the effects of androgens on lipolysis are relatively little known in the female sex, we decided to examine this aspect by treating ovariectomized and intact female rats with testosterone. Materials and Methods Chemicals[125]cyanopindolol (2220 Ci/mmol) was from the Radiochemical Centre (Amersham, UK). Collagenase type I, bovine serum albumin, forskolin, isoproterenol bitartrate, epinephrine bitartrate, norepinephrine bitartrate,

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Section: Discussionsupporting

confidence: 91%

Testosterone treatment of ovariectomized rats: Effects on lipolysis regulation in adipocytes

Pergola

Holmäng

Svedberg

et al. 1990

Acta Endocrinologica

View full text Add to dashboard Cite

show abstract

“…The similarity of the quantitative stimulation of lipolysis by isoproterenol and norepinephrine within all the experimental groups suggests that a 2 -adrenergic inhibition of lipolysis is weak, perhaps nonexistent, and is not affected by androgens in rats (10). The problem of the existence of a 2 -adrenoceptors in rat adipocytes still remains to be conclusively resolved (22)(23)(24).…”

Section: Discussionmentioning

confidence: 95%

Testosterone Increases Lipolysis and the Number of β-Adrenoceptors in Male Rat Adipocytes*

Xu¹,

Pergola²,

Björntorp³

1991

Endocrinology

183

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The influence of androgen status on the regulation of lipolysis and number of beta-adrenoceptors in isolated adipocytes was studied in male rats. Castration resulted in decreased catecholamine-induced as well as forskolin-induced lipolysis. beta-adrenoceptor number, examined by a whole cell cyanopindolol binding assay, was also diminished to a similar extent. Testosterone treatment of castrated rats normalized lipolysis as well as beta-adrenoceptor number. These results demonstrate that testosterone stimulates catecholamine-induced lipolysis in vivo by increasing the number of beta-adrenoceptors as well as the activity of adenylate cyclase, confirming previous in vitro studies performed in adipose precursor cells.

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“…Although « 2 -adrenergic receptors are present in mature rat adipocytes (22), their inhibitory effect on lipolysis is not influenced by androgen administration (8). These results, then, also strengthen the conclusion that T is active only via an increase in /3-adrenergic agonist-binding capacity.…”

Section: Discussionmentioning

confidence: 99%

The Effects of Androgens on the Regulation of Lipolysis in Adipose Precursor Cells

Xu¹,

Pergola²,

Björntorp³

1990

Endocrinology

191

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Adipose precursor cells from male rats were exposed in primary culture to testosterone (T) or dihydrotestosterone (DHT), and their effects on the regulation of lipolysis were studied. T, but not DHT, stimulated catecholamine-induced lipolysis in a dose-dependent manner, including physiological concentrations. The effect was equally pronounced with isoproterenol (a pure beta-adrenergic agonist) and norepinephrine (a mixed alpha 2- and beta-adrenergic agonist). The higher lipolytic capacity of catecholamines on T-treated cells was paralleled by a similar increase in the number of beta-adrenoceptors in the cells, without a change in the receptor affinity, suggesting that T induced new synthesis or externalization of beta-adrenoceptors. Both T and DHT stimulated forskolin-induced lipolysis, suggesting an androgen effect at the level of the catalytic subunit of adenylate cyclase. The pertussis toxin-stimulated lipolysis was not influenced by the presence of androgens in the culture medium, and no effect was seen on the antilipolytic effect of insulin. These effects did not disappear in the presence of an aromatase inhibitor, suggesting that the T effects were not mediated by conversion to estrogens. These cells showed specific saturable binding for androgens, with a Kd in the range of androgen concentrations shown to be active. In conclusion, androgens enhance the lipolytic capacity of these cells by increasing the apparent number of beta-adrenoceptors (T only) and the activity of adenylate cyclase (both T and DHT). These changes are not mediated by conversion to estrogens. These effects probably occur via binding to specific androgen receptors.

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Evidence of functional α2-adrenergic receptors in adult-rat adipocytes by using the agonist UK 14304

Cited by 15 publications

References 23 publications

Testosterone treatment of ovariectomized rats: Effects on lipolysis regulation in adipocytes

Testosterone treatment of ovariectomized rats: Effects on lipolysis regulation in adipocytes

Testosterone Increases Lipolysis and the Number of β-Adrenoceptors in Male Rat Adipocytes*

The Effects of Androgens on the Regulation of Lipolysis in Adipose Precursor Cells

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