This prospective interventional study was carried out on 50 male adult Wistar rats with a weight of 200±20 gm which were obtained from Pasteur Institute of Iran. This study was carried out between October 2017 and January 2018. The average weight of each cage was kept similar. The temperature was at 22±2°C and animals were kept under the condition of half light and half darkness (light on at 08:00 am). Animals had free access to water and standard laboratory chow. The protocol was approved by Tehran University of Medical Sciences Ethics Committee which is registered under the registration number IR.TUMS.VCR.REC.1397.186, and it conformed to the provisions of the World Medical Association’s Declaration of Helsinki.

Animals were randomly assigned to five groups with 10 rats in each group according to the study design below; Group 1, comprised the control group maintained under experimental conditions, without any injection. Group 2, received normal saline, to provide the same psychological conditions with control group, both groups were injected simultaneously. Based on animal physiological guidelines, three groups received 2, 4 and 6 mg/kg of oxymorphone, which contains the suitable drug dose for injection [12,15]. The bulk oxymorphone (Extended release) powder was dissolved in 900 mL phosphate buffered saline1X (PBS) by heating (45°C with gentle agitation) to achieve different concentrations of stock solution. Bolus solution was centrifuged (10,000 gm for 25 minutes) to remove large undissolved aggregates. During the experiment the animals were healthy and were repeatedly screened. Injections were administered intraperitoneally via a catheter once a week for 56 days. After eight weeks, blood samples were collected using cardiac puncture method. Sera were collected and quantified for enzymes including CK, ALP, AST and ALT levels using standard automated spectrophotometer especially photometric kinetic methods based on the German Biochemical Society (Beckman DU-6, Fuller-ton, CA) [16].

All the chemicals had the highest purity (95%). Experiments were performed at 37^oC, and as time required evaluating reaction rates must be atleast three times, the enzymatic and hormonal OD at 1, 2 and 3 minutes was recorded. Hormones including ACTH, TSH, T3, T4, Cortisol and Aldosterone levels were quantified using the enzyme-linked immunosorbent assay (ELISA). ELISA kits for ACTH, TSH, T3, T4, TSH and Cortisol were purchased from Sigma- Aldrich (St. Louis. Missouri). ELISA kit for Aldosterone was purchased from Cayman (Cayman Chemicals, Ann Arbor, MI).

All values are presented as mean±SEM. Statistical significance were evaluated by one-way analysis of variance (ANOVA, t-test) using IBM SPSS Statistics 20.0 for Windows. Differences with p<0.05 were considered as significant.

The results demonstrate that serum levels of ACTH increased in all groups which received oxymorphone. These changes were more significant than control group (p-value <0.001) as well as groups that received saline (p-value <0.01).

As the results in [Table/Fig-1], the higher amount of oxymorphone leads to the greater quantity of ACTH.

The [Table/Fig-1] illustrates that, in all groups that received oxymorphone, the cortisol levels significantly increased, which were near 10 times more than control group (p<0.001) and normal saline group (p<0.001). Thus, the higher amount of oxymorphone may lead to increased serum levels of cortisol.

With the treatment of oxymorphone in different doses, the serum levels of aldosterone raised up. The groups that received 2 mg/kg and 4 mg/kg of oxymorphone had significantly increased Aldosterone in comparison to control and normal saline group (p<0.001). The last group which received 6 mg/kg of oxymorphone also had a significant increase in aldosterone serum levels (p<0.01) [Table/Fig-1].

The mean serum levels of CK in the control group were 427±30.5. In contrast, the mean serum levels of CK in experimental groups were 299.8±28.57 (group treated with 2 mg per kg of oxymorphone, p<0.05 in comparison with control group), 134.2±12.44 (4 mg/kg, p<0.001 in comparison to normal saline received group) and 201±17.39 (6 mg/kg, p<0.01 compared with normal saline group) which had significant decrease in all exposed groups in comparison to control or normal saline groups [Table/Fig-1].

Results illustrated that, treatment by oxymorphone significantly increased serum levels of TSH in all three groups compared to control group (p<0.05). The statistical details of the serum levels of TSH are shown in [Table/Fig-1]. Oxymorphone had no statistically significant impact on the serum levels of ALP. Serum levels of ALT had a significant change in group which received 6 mg/kg of oxymorphone (p<0.01). Other groups did not have a definite change. Serum levels of AST had a significant increase in 6 mg/kg oxymorphone received group (p<0.05). Rest of groups were unchanged. The statistical details for this section are presented in [Table/Fig-2].

Serum level of T3 was influenced by 6 mg/kg of oxymorphone, which was significantly decreased in comparison to control group with p<0.01. Other groups didn’t indicate meaningful change [Table/Fig-3]. Whereas, serum levels of T4 were affected by 4 and 6 mg/kg of oxymorphone treatment compared with control group (p<0.01). However, 2 mg/kg oxymorphone received group had no significant change [Table/Fig-3].

In the present study, the changes in biochemical parameters in response to the injection of oxymorphone in adult male rats, which could cause harmful effects on the involved organs were evaluated.

It was observed that, significant elevation in the quantity of ACTH, cortisol and aldosterone in rats serum exposed to different concentrations of oxymorphone. Increase in amount of ACTH in the plasma may represents a disorder in the pituitary gland function because ACTH is a tropic peptide hormone secreted from the anterior pituitary gland [7], and also elevation in the quantity of ACTH has a subsequent effect on the increase of cortisol hormone, because the role of ACTH in the hypothalamo-pituitary axis includes stimulating the release of cortisol from the adrenal glands (the HPA system) [17,18], and also the increase in ACTH in the serum cause the increase in aldosterone, because ACTH is one of the principal regulators of adrenal aldosterone biosynthesis [19]. One of the other reasons for increased amount of cortisol in plasma could be abnormality in the adrenal gland function; hyperaldosteronism being associated with renal failure [20]. The significant changes in the activity of these enzymes in blood plasma may indicate side effects of oxymorphone on renal, pituitary and adrenal gland functions or enzymes secreted by these organs. Therefore, these patients are more vulnerable to taking oxymorphone. Patients with Cushing’s syndrome, who also experience increased cortisol levels [21], should stop using oxymorphone drugs because excessive cortisol increases digestive problems and causes heart disease. And also, in people with hyperpituitarism [22] or pulmonary tumours [23] taking an oxymorphone pill is not recommended because of an increase in ACTH serum levels.

We also observed significant decrease in Creatine Kinase (CK) in the serum from all groups which received injection oxymorphone. CK is an enzyme found in the heart, brain, skeletal muscle, and other tissues, and decrease in CK may be found as a consequence of diminished efflux of the muscle enzyme into serum from reduced physical activity caused by illness or advanced age [24], in pregnant women (in the first months of pregnancy) [17], or in some disease such as polymyositis and dermatomyositis [18], Rheumatoid arthritis (RF) [19], and also liver diseases caused by alcohol [20]. From this, it can be concluded that, taking of oxymorphone pill puts these people at risk.

In the present study, the liver enzyme activities (serum aminotransferases, including ALT and AST) that are critical in the diagnosis and assessment of liver disease, ALT significantly decreased and AST significantly increased in 6 mg/kg oxymorphone received group. These results indicate possible liver dysfunction as a result of given maximum dose of oxymorphone, which reduces the amount of liver enzymes. Patients with liver dysfunction and patients who use cholesterol-lowering statin drugs such as lipitor, pravachol and mevacor the oxymorphone drug metabolism may be altered [25]. Given the fact that alcohol abusers, patients with non-alcoholic liver disease, hepatitis, cirrhosis, dermatomyositis, cytomegalovirus infection, and celiac patients are at increased serum AST levels, the use of oxymorphone for these groups might be dangerous [26].

The serum levels of TSH significantly increased in oxymorphone treated rats; TSH induces the thyroid gland to produce T3 and T4. In these conditions, which was similar to the early hypothyroidism (thyroid dysfunction), the low levels of T3 and T4 are the main trigger for TSH secretion [27]. These two hormones are involved in wide range of metabolic activities influencing the growth and development of organisms, and primarily involved in energy production by increasing the metabolic rate [21-23]. So, disruption of these hormones indicates a thyroid dysfunction and has harmful effects on the growth and development. Thus, it was concluded that although oxymorphone seems to be effective in pain control, their toxic side effects should be considered.

Although this research was carefully prepared, certain limitations were inevitable. These include time and finance. It is suggested that future studies should be done for a longer time, with higher doses. Moreover, the study could be done on histological characteristics to assess the effect of this drug.

In this study, various biochemical parameters were assessed after oxymorphone injection in rats by using photometric kinetic methods that included ELISA and spectrophotometry. Serum levels of ACTH, cortisol and aldosterone had significant changes in all groups which received oxymorphone. With the treatment of oxymorphone at 6 mg/kg done, the serum levels of ALT, AST and T3 were found raised. In conclusion, oxymorphone injection has a significant impact on biochemical parameters. Therefore, three groups of patients, including patients with liver disorders, alcoholism, and people who suffer from heart failure are more likely vulnerable and it’s better to stop taking oxymorphone pill. However, more human studies should be done in this regard to confirm this finding.