Regulation of Adipocyte Proliferation by Insulin and Luteinising Hormone.

David Cadagan1, Christopher Towlson2, Stephen Merry1. 1Staffordshire University, Stoke on Trent, UK, 2Nottingham University, Nottingham, UK

The overall aim of this pilot study was to examine whether the inhibitory effects of luteinising hormone (LH) on adipocyte proliferation is influenced by insulin treatment.

The inhibitory effects of LH on cell proliferation have been noted in different cell types, including Leydig [1] ovarian and mammary epithelial cells [2, 3]. More recently, we have determined this effect to also be true within adipocytes. With the reductions in serum LH associated with increased BMI, it is important to examine this adipocyte regulatory mechanism in order to understand endocrinopathies including metabolic syndrome, Polycystic ovarian syndrome (PCOS)and diabetes.

With increases in insulin secretion also often associated with these conditions and the knowledge that the combined effect of insulin and LH stimulates metabolic activity in cells of the adrenals [1] and ovaries [4]; the importance of the combined effect of LH and insulin on adipocyte proliferation is necessary in the understanding of this regulatory mechanism and where dysfunction may therefore occur.

The 3T3-L1 preadipocyte mouse cell line (N=3) was used in this pilot study and cultured under in-vitro conditions to be analysed using a 5-day MTT proliferation assay. We examined proliferation under 3 treatments: (LH / LH + insulin / media alone).

Results have shown significant decreases in proliferation between no treatment and both LH (p <0.0187) and LH / insulin treatment groups (p <0.0142), as determined using un-paired t-test.

No significant variation was seen in adipocyte proliferation when treated with insulin + LH against LH treatment alone.

In conclusion our pilot study suggests that the inhibitory effects of LH are not reduced with the addition of insulin. This mechanism may lead to novel areas of examination in conditions involving reductions in circulatory LH and its association to weight gain and diabetes. This study also allows an insight into further understanding adipocyte metabolism. Collection and analysis is ongoing.

1. Sriraman, V., et al., Effect of deprival of LH on Leydig cell proliferation: involvement of PCNA, cyclin D3 and IGF-1. Mol Cell Endocrinol, 2000. 162(1-2): p. 113-20.

2. Ivarsson, K., et al., Diverse effects of FSH and LH on proliferation of human ovarian surface epithelial cells. Hum Reprod, 2001. 16(1): p. 18-23.

3. Sharoni, Y., et al., Inhibition of growth of human mammary tumor cells by potent antagonists of luteinizing hormone-releasing hormone. Proc Natl Acad Sci U S A, 1989. 86(5): p. 1648-51.

4. Campbell, B.K., D.T. Baird, and R. Webb, Effects of dose of LH on androgen production and luteinization of ovine theca cells cultured in a serum-free system. J Reprod Fertil, 1998. 112(1): p. 69-77.