Reprod. Nutr. Dev. 43 (2003) 567-576
DOI: 10.1051/rnd:2004009

Metabolic effects of dietary lactose in adult female rats

Gentao Liu^a, Claude L. Hughes^{b, c}, Ruchi Mathur^d, Warren G. Foster^{a, e}, Vicki L. Davis^{a, f} and Denis A. Magoffin<sup>a

a</sup>  Cedars-Sinai Burns and Allen Research Institute, Cedars-Sinai Medical Center/University of California Los Angeles School of Medicine, CA, USA
^b  Department of Obstetrics and Gynecology, Duke University Medical Center, NC, USA
^c  Department of Medical & Scientific Services, Quintiles, PO Box 13979, Research Triangle Park, NC 27709, USA
^d  Department of Medicine, Keck School of Medicine, University of Southern California, CA, USA
^e  Obstetrics & Gynaecology, McMaster University Medical Center, Hamilton, ON, Canada
^f  Duquesne University, Pittsburgh, PA, USA

Received 23 March 2003; accepted 30 September 2003

Abstract - As an outgrowth of our interest in the potential toxicity of dietary galactose, we investigated the metabolic effects of high lactose diets in Long-Evans female rats. Seventy-five Long-Evans female rats (25-day-old) were randomized to receive one of 3 diets for 7 months: glucose diet (CON); low lactose diet (10.5%, LLD); or a high lactose diet (41.9%, HLD). Necropsy was performed seven months after randomization. HLD animals had significantly lower body weights than controls ( P < 0.01). These animals continued to grow, however at a retarded rate compared to the CON group. The HLD group also had significantly lower triglyceride and non-esterified fatty acid levels than the CON group ( P < 0.01 and P < 0.05). Serum glucose concentrations were lower in the HLD group compared to CON animals ( P < 0.05), while serum insulin levels were lower than both the LLD and CON animals ( P < 0.01 and P < 0.05). Leptin exhibited a similar trend. Thyroid studies revealed no difference in TSH between groups. Free T4 was significantly higher in HLD rats compared to LLD and CON rats while free T3 was lower in the HLD group ( P < 0.05). This indicates a possible impairment in T4 to T3 conversion. Our data suggests that a long-term high lactose diet is associated with a decrease in insulin and leptin levels, and an increase in the insulin to glucose ratio. However, these changes are seen in the presence of a decreased body mass. A significant effect on thyroid hormone metabolism is also seen, and may be an adaptive mechanism in lactose-fed rats.

Key words: lactose / galactose / rat / thyroxine / thyroid metabolism

Corresponding author: Claude L. Hughes Claude.Hughes@quintiles.com

© INRA, EDP Sciences 2003