A Comparative Study Indicates Methimazole Induced Chemical Hypothyroidism Causes Inhibition of Pineal Gland Karyomorphology in Three Different Species of Animals

In the present investigation, influence of experimentally induced hypothyroidism on pineal karyomorphology was studied in three different species of animals – post pubertal male mice (Mus musculus), adult male rats (Rattus rattus) and neonatal male chicks (Gallus domesticus). Twenty-two animals of each species group were used, divided into two sets of experimental groups, Group A the control group and the other Group B the treated group. In Group A, eleven control animals of each species were given normal pelleted feed and normal drinking water ad libitum. In GroupB, the adult male mice (N=11), rats (N=11) and chicks (N=11) were supplied with normal pelleted feed and methimazole dissolved in drinking water (at a dose of 1 gm/l). After expiry of the experimental period of fifteen consecutive days each set of control and treated animals were divided into two groups and killed by etherisation. In the first set of control (N=6) and treated (N=6) experiments, animals were considered for histological studies. The second set of control (N=5) and treated (N=5) experiments, animals were considered for T4 assay. Present data reveal that methimazole caused a significant reduction reaching about detection value of serum T4 (μg/dl) levels in all the three species of animals. Such hypothyroid animals showed inhibition of the pineal gland activity as seen from significantly decreased pinealocyte nuclear diameter (μm) in all three species of animals, along with an increased pinealocyte nuclear density per microscopic field in mice and rats. Our study indicates that methimazole induced chemical hypothyroidism inhibits pineal gland activity in both mammals and birds.