(1987, 1988, 1990, 1997a. b & 1998) and Parada et af. (1 988 & 1989). ... 1992; Parada et al. 1988), and an .... lyzed by the chi square test. Differences were ...
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0 Phurmaculogy & Toxicology 1998. 83, 57-61.
PharmacologyQToxieology
Printed in Denmark . All rights reserved
ISSN 0901-9928
Glucose Tolerance and Serum Insulin Levels in an Animal Model of Obesity Induced by the Antipsychotic Drug, Sulpiride Trino Baptista, Anny LaCruz and Luis Hernandez
Department of Physiology, Medical School, Los Andes University, PO. Box 93, MCrida, 5101-A, Venezuela (Received December 9, 1997; Accepted March 12, 1998) Ahsfruct: To assess the role of insulin in the development of obesity induced by antipsychotic drugs, a glucose tolerance test was conducted in 40 female rats during the peak of sulpiride-induced weight gain and in 40 vehicle-treated animals. The glucose area under the curve did not differ between the groups (P=0.24), however, the area under the insulin curve was significantly decreased by sulpiride (55.252.8 versus 115.6t 18.9, P=0.007). The results suggest that insulin resistance and hyperinsulinaemia are not involved in the excessive weight gain observed in this animal model of drug-induced obesity. Alternatively, the insulin-dampened response observed in the sulpiride-treated rats may be related to increased insulin sensitivity, which may promote weight gain as proposed by Ravussin (1995).
Excessive weight gain is a serious side effect of long-term administration of neuroleptics or antipsychotic drugs in psychiatric patients (Bernstein 1992; Bhavnani & Levin 1996). The presence of metabolic-endocrine abnormalities (Oades & Schepker 1994) and appetite disturbances (Robinson et al. 1975) which are independent of drug administration, have hampered the clarification of the mechanisms involved in the drug-induced weight gain in humans. Therefore, an animal model has been developed by Baptista et al. (1987, 1988, 1990, 1997a. b & 1998) and Parada et af. (1 988 & 1989). Chronic administration of sulpiride, trifluoperazine, thioridazine or haloperidol induces obesity in female but not in male rats (Baptista et al. 1987 & 1988; Parada et al. 1989; Shimizu et al. 1990). The mechanisms have been explored in depth with sulpiride, a D2-D3 dopamine receptor antagonist, because it is devoid of significant motor and sedative effects (Wagstaff et al. 1994). At least two pharmacological effects of neuroleptics may mediate the excessive weight gain: a neurogenic effect which involves a direct stimulation of appetite through the blockade of dopaminergic and serotonergic receptors in the lateral hypothalamus (Baptista er al. 1987 & 1990; Bernstein 1992; Parada et al. 1988), and an endocrine effect related to the drug-induced hyperprolactinaemia (Baptista et al. 1997 a & d, 1998; Correa et a/. 1987; Parada et al. 1989). Prolactin plays an important role in body weight regulation in female mammals. For instance, a linear positive relationship between body weight and prolactin serum levels has been demonstrated in healthy premenopausal women (Wang et al. 1987). In addition, excessive body weight gain is often detected in hyperprolactinaemic conditions in female rats (Moore et al. 1986; Gerardo-Gettens et al. 1989) Author for correspondence: Trino Baptista, Apartato 93, Merida, 5101-A, Venezuela (fax 58-74-638304).
and in women (Creemers et al. 1991; Ferreira et al. 1995). The mechanisms by which hyperprolactinaemia stimulates appetite have not been clarified, but they could be related to the impairment in the gonadal production of oestradiol (Baptista et al. 1997 c & d; Dorrington & Gore-Langton 1981; Parada et al. 1989). The decrease in oestradiol serum levels affects the oestradiol/testosterone ratio, which modify the functioning of satiety-related neurones in the ventromediaVparaventricular hypothalamus and in the long-term increases in food consumption and body weight (Wade & Schneider 1992). In vitro experiments have shown that hyperprolactinaemia also impairs the insulin sensitivity in the adipocytes (Cabrera er al. 1988). The insulin resistance and the subsequent hyperinsulinaemia, if physiologically relevant in the whole organism, might be a contributing factor to the excessive weight gain (Kissebah & Krakover 1994). Preliminary reports suggest that in fact, a trend toward glucose intolerance is detected in people under chronic antipsychotic administration (Beumont & Bergen 1982; Erle et al. 1977; Foss et al. 1995). however its relationship to the drug-induced weight gain has not been explored. The purpose of this study was to assess whether or not hyperinsulinaemia and/ or glucose intolerance is detected in rats rendered obese by sulpiride. For this purpose, a glucose tolerance test was conducted during the period of maximal weight gain and hyperphagia. Additionally, the serum prolactin and oestradiol levels, and the cytological vaginal cycle were also assessed. Materials and Methods Animals. Eighty adult female rats of the Wistar strain weighing 200250 g were individually housed under a 12/12 hr light/dark cycle, with lights on at 7 a.m. A high fat diet (66.6% powdered chow
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TRINO BAPTISTA ET A L
pellets, 33.3 corn oil %) was placed in spill-proof feeders; food and water were available ad libitum. Body weight and food intake were daily assessed to the nearest 0.1 g. In half the rats of each treatment group the vaginal smear (cell morphology) was daily assessed by light microscopy throughout the experiment. Accordingly, each rat was labeled as having a normal (three consecutive 4-day oestrousperiods) or abnormal cycle (permanent dioestrous).
lation coefficient was used to correlate body weight gain, insulin and glucose levels in each group. The vaginal cycle data was analyzed by the chi square test. Differences were considered significant when Ps0.05.
Drug administration. After one week of adaptation to the housing and diet conditions, the animals were matched by weight and divided into two groups of 40 rats each. At 9 a.m. one group received a single daily dose of sulpiride (Sigma, 20 mg/kg/intraperitoneally) and the other group received an injection of vehicle (0.1NHC1, with pH 7 adjusted with 0.1N NaOH).
Sulpiride induced a significant body weight gain (fig. 1). The mean body weight (g) for the sulpiride and vehicle group respectively were: initial weight: 24323 versus 24322, nonsignificant; final weight: 26353 versus 25054, t (78)=2.1, P=0.037. Food intake was significantly enhanced as well (data not shown): f (1, 702)=6.36, P=0.013. The area under the glucose curve did not differ in the two groups, however the insulin area was significantly lower in the rats treated with sulpiride (fig. 2). No correlation was found between body weight gain after 10 days of treatment and the serum glucose or insulin levels in any group of rats: for the 30 min. point of the tolerance curve: sulpiride group: weight gain and insulin: r=0.01, P=O.9; weight gain and glucose: r=0.06, P=0.8; vehicle group: weight gain and insulin: r=0.37, P=0.2; weight gain and glucose: r=0.4, P= 0.08.
Glucose tolerance test. Previous experiments have shown that the maximal weight gain and hyperphagia during sulpiride treatment occurs at the second week of treatment, then they level off (Baptista et al. 1987, 1988, 1997 a & c). Therefore the glucose tolerance test was conducted after 10 days of sulpiride administration. For this purpose: the rats were deprived of food for 8 hr, and were decapitated in order to obtain blood from the trunk vessels in basal conditions or 30, 60 and 90 min. after a single glucose overload (2 g/kg/intraperitoneally). In a separate group of rats, prolactin and oestradiol serum levels were measured in fasting conditions after ten days of sulpiride (n= 11) or vehicle administration (n= 1I). Serum glucose was assessed by an enzymatic method from Boehringer (Mannheim, Germany); insulin, prolactin and oestradiol serum levels were assessed by radioinmunoassay with commercial kits (DPC, Los Angeles, CA, USA); the inter- and intra-assay variation was less than 10%.
Results
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Statistical analysis. Body weight gain and food intake comparisons between the sulpiride and vehicle group were conducted by a twoway ANOVA for repeated measures. The glucose and insulin areas under the curve, oestradiol and prolactin levels in the two groups were compared by a two-tailed t-test for unrelated samples. A corre-
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Days Fig. 1, Body weight gain in rats treated during 10 days with sulpiride (20 mg/kg/intraperitoneaIly, n=40) or vehicle (0.25 cdintraperitoneally, n=40). Sulpiride significantly increased weight gain; treatment effect: f (1, 624)=70, P=O.OOOl, time effect: f (8, 624)=23, P= 0.0001. Values represent mean5S.E.M.
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Time (minutes) Fig. 2. Glucose and insulin serum levels in basal conditions and after a glucose overload in sulpiride or vehicle treated rats. Each point represent the mean2S.E.M of 10 rats. The area under the insulin curve was significantly lower in sulpiride treated animals than in the vehicle controls: 55.252.8 versus 115.6519.8, t (18)= 3.01, P=0.0075. No significant differences were observed in the area under the glucose curve: sulpiride group: 248.325.5; vehicle group: 259.8k7.8, t (18)=1.2, P=0.24.
ANTIPSYCHOTICS AND INSULIN Table 1.
Serum levels of oestradiol and prolactin after two weeks of treatment with sulpiride or vehicle.
Oestradiol (PdW Prolactin (ndml)
Sulpiride n=ll
Vehicle n=ll
t
7.12?0.58
9.01% 1.08
NS
100.1232.9
3.92 1.06
2.5*
Values represent mean2S.E.M. (*)=P
