**1. Introduction**

Diabetes mellitus is a chronic metabolic dysfunction which involves alterations in insulin production. Pancreatic β cells are primarily responsible for insulin secretion. There is a variety of complications associated with this disease such as chronic hyperglycemia, neuropathy, retinopathy, and cardiovascular diseases. Diabetes mellitus may be divided into three types: diabetes mellitus type 1 (DM1), type 2 (DM2), and type 3 (DM3)—also known as gestational diabetes mellitus. DM1 is based on an immune-mediated destruction of β cells. It is an autoimmune disease, most common in children and young adults. The treatment includes monitoring of blood glucose levels and insulin therapy [1, 2]. DM2 is associated with insulin resistance. The main cause is a reduced sensitivity of affected tissues to the metabolic effects of insulin. The development of the disease is often associated with obesity, which, on the other hand, causes health complications, such as fertility issues. Contraindications associated with DM2 include disorders of the male reproductive system because metabolism of glucose is essential for a correct process of spermatogenesis. DM2 has a negative impact on the sperm quality markers such as motility, DNA integrity, and seminal plasma composition [3, 4]. Development of DM3 is mostly common among women who are overweight or obese in comparison with thin or normal-weight women. This type of diabetes

may cause higher levels of adipose tissue in the fetus and an increased child birth weight. Also a few studies reported that DM3 is associated with higher levels of abdominal fat and an increased risk for visceral adiposity which could be linked to other consequences following birth such as future development of DM2 and cardiovascular diseases [5, 6].

Another factor that negatively affects male fertility is obesity. Obesity has been shown to negatively affect the male reproductive potential not only by decreasing sperm quality but mainly by altering the germ cell molecular structure in the testes [7]. Animal models play a pivotal role in monitoring and understanding DM pathogenesis due to a combination of their genetic and functional characterization [8]. Suitable models to demonstrate the effects of DM2 on the organism are Zucker diabetic fatty (ZDF) rats. This type of rats had been discovered in 1961 following cross-breeding of Merck (M-strain) and Sherman rats. ZDF rats have the unique ability to simulate symptoms and contraindications of DM2. These rats have insulin resistance caused by the presence of homozygous mutation of the leptin hormone receptor (*fa gene*) which causes obesity and an increased insulin secretion [9, 10]. The aim of this chapter was to evaluate the effect of diabetes mellitus type 2 on the vitality of ZDF rat reproductive cells.
