Effect of 131I-induced hypothyroidism on indices of reproductive function in adult male dogs

Preparation of Levothyroxine Transdermal Gels and Preliminary Pharmacokinetic Study in Hypothyroidism Rat Model

Background:

Hypothyroidism is a common disorder due to inadequate thyroid hormone secretion. In patients with hypothyroidism, levothyroxine (LT4) is the treatment of choice, and tablets are the most common dosage form. However, the main limitation of tablet LT4 is malabsorption.

Objective:

This study intends to develop a new dosage form of percutaneous drug delivery for levothyroxine. Absorption of levothyroxine sodium through the application of gel formulation was studied using a hypothyroidism rat model.

Methods:

A formulation of levothyroxine sodium gel was developed and selected. In-vitro transdermal experiments were performed using the vertical Franz diffusion pool method, and gel formulation was used for animal research (hypothyroidism rats model). Total 30 rats were randomly divided into 6 groups, and one was the normal control group. The other 5 groups were prepared as hypothyroidism models. After applying different doses of gel preparation to the rat model, we measured serum total thyroxine (TT4), free triiodothyronine (FT3), free thyroxine (FT4), and thyroid-stimulating hormone (TSH) using fluorescence determination of luminescence immunoassay.

Results:

The optimum formulation of levothyroxine gels comprised 20% polyvinyl alcohol (PVA), 5% glycerol, 2% azone, and 6% oleic acid. The application of levothyroxine sodium gel resulted in quick and smooth action so that the predicted level of the normal control group could be reached within 2 weeks, and it lasted steadily for 8 weeks.

Conclusion:

This research study successfully developed and tested an optimal formulation of levothyroxine gel with therapeutic benefit on hypothyroidism in rats.

The effect of 131I-induced hypothyroidism on the levels of nitric oxide (NO), interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-α), total nitric oxide synthase (NOS) activity, and expression of NOS isoforms in rats

Accumulating evidence has shown that hypothyroidism affects the cardiovascular system, significantly increasing the incidence of cardiovascular diseases. In the present study we investigated the effect of radioactive iodine (I-131)-induced hypothyroidism on several parameters of vascular function, such as nitric oxide (NO), total nitric oxide synthase (NOS) activity and expression of NOS isoforms, as well as on interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-α) as indicators of inflammation, in rats. A dose of 150 µCi of 131-I was determined as optimal for establishing the model of hypothyroidism in rats. After administration of 131-I, at the end of month 1, 2, and 4 (n = 3 for each time point), NO, IL-6, and TNF-α in the serum and total NOS activity in the aorta were determined in 150 µCi group, compared to controls. The mRNA and protein expression of endothelial, neuronal, and inducible NOS (eNOS, nNOS, and iNOS) in the rat aorta was also estimated, using quantitative reverse transcription polymerase chain reaction and Western blot, respectively. The levels of IL-6 and TNF-α increased in 150 µCi group; the results were significant at the end of month 2 and 4 for IL-6, and at all time points for TNF-α. The levels of NO decreased significantly at the end of month 2 and 4 in 150 µCi group. The total NOS activity increased significantly in 150 µCi group, at all three time points. Significant changes in the mRNA and protein expression of all three NOS isoforms were observed in 150 µCi group compared to controls. NO, IL-6, TNF-α levels and NOS activity and expression are altered in hypothyroid state, and the underlying mechanism should be further investigated.

Canine and feline pregnancy loss due to viral and non-infectious causes: a review

Among the causes for pregnancy loss, viruses and non-infectious factors are among the most important. In both dogs and cats, research and clinical evidence provide proof that there is an increasing incidence of pregnancy loss associated with infectious diseases like herpesvirus, as well as the presence of toxicants or chemicals in the animal's diet and environment. Endocrine causes must be taken into consideration when dealing with pregnancy loss. This review will cover the most recent knowledge regarding viral and non-infectious of pregnancy losses in the dog and cat.