Cimetidine and HDL cholesterol

Secondary causes of hyperlipidemia

Secondary causes of hyperlipidemia are important to recognize. In fact, hyperlipidemia may be a clue to the presence of an underlying systemic disorder. It may greatly heighten the risk of atherosclerosis with a raised LDL-c, triglyceride-rich lipoprotein excess, and increased lipoprotein(a) as well as lowered HDL-c. The search for secondary causes may provide a clue as to why patients with primary lipid disorders suddenly develop worsening lipid profiles. The point is a crucial one because some acquired causes of hyperlipidemia, such as alcohol, estrogens, steroids, or pregnancy, when superimposed on a primary familial form of hypertriglyceridemia can result in a saturated removal system and a buildup of chylomicrons, which can lead to life-threatening pancreatitis. A convenient way to remember secondary causes is to think of the four D's of diet, drugs, disorders of metabolism, and diseases. Although diets rich in saturated fats and cholesterol are a common cause of the mild hypercholesterolemia seen in our society, alcohol excess and weight gain can explain much of the tendency toward hypertriglyceridemia. Interestingly anorexia nervosa has long been associated with severe but reversible hypercholesterolemia. Several classes of drugs need to be considered as common causes of altered lipid profiles. Glucocorticoids and estrogens elevate triglycerides and raise levels of HDL-c. Anabolic steroids taken orally markedly reduce levels of HDL-c in contrast to injectable testosterone, which does not adversely affect the LDL-to-HDL ratio. Oral contraceptives affect atherosclerotic risk depending on the kind and doses of progestin/estrogen. In those with an underlying primary hypertriglyceridemia and associated obesity, estrogenic medications can depress triglyceride removal mechanisms, leading to the chylomicronemia syndrome and pancreatitis. Antihypertensives have variable effects on lipids and lipoproteins. Although short-term thiazide usage raises cholesterol, triglycerides, and LDL-c, long-term usage is not necessarily associated with significant alterations in lipid levels. Alpha blockers may cause an increase in HDL-c, whereas beta blockers raise triglycerides and lower HDL-c. Sympatholytics, angiotensin converting enzyme inhibitors, and calcium channel blockers are essentially lipid neutral. Retinoids can be associated with increased LDL-to-HDL ratios and occasionally striking elevations in triglycerides. Cyclosporine raises LDL-c and lipoprotein(a). Classes of drugs that may raise HDL-c include cimetidine, antiepileptic drugs, and tamoxifen, but the effect may be seen primarily in women. Hypothyroidism is the most common secondary cause of hyperlipidemia after dietary causes are considered. A thyroxine and TSH level should be obtained on all new cases of clinically important hyperlipidemia.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of cimetidine on the oxidative metabolism of estradiol

Cimetidine, a histamine H2-receptor antagonist widely used to treat peptic ulceration, is known to cause gynecomastia and sexual dysfunction in some men. Since cimetidine inhibits the cytochrome P-450-dependent biotransformation of numerous drugs, we investigated the possibility that it might also inhibit the cytochrome P-450--dependent metabolism of estradiol. Radiometric analysis of urine and serum samples from nine normal male volunteers showed that the extent of 2-hydroxylation of estradiol was significantly reduced from a mean (+/- SEM) of 31.7 +/- 2.3 percent to 19.7 +/- 2.3 percent (P less than 0.0001) after two weeks of oral treatment with cimetidine (800 mg twice a day); the 16 alpha-hydroxylation of estradiol was unaffected. At the same time, the urinary excretion of 2-hydroxyestrone decreased by approximately 25 percent (P less than 0.0002), and the serum concentration of estradiol increased by approximately 20 percent (P less than 0.04). The mean percentage of estradiol 2-hydroxylation was also rapidly reduced, from 36.8 +/- 4.4 percent to 24.5 +/- 3.4 percent in six men after one week of oral cimetidine at a lower dosage (400 mg twice a day; P less than 0.0006). In a separate study of seven men, ranitidine, a second-generation H2-receptor antagonist, was found to have no effect on the 2-hydroxylation of estradiol. This study demonstrates that the administration of cimetidine to men decreases the 2-hydroxylation of estradiol and results in an increase in the serum estradiol concentration. This mechanism may help to account for the signs and symptoms of estrogen excess reported with the long-term use of cimetidine.

Histamine H2-receptor antagonists and high-density lipoproteins

Epidemiologic evidence has shown that elevated levels of high-density lipoproteins (HDL) protect against the development of coronary heart disease (CHD). These observations have prompted the evaluation of various factors thought to affect HDL and its subspecies, HDL2 and HDL3. Numerous behavioral and physiologic factors have been shown to elevate HDL levels. These are currently being researched as potential tools in preventing CHD. Several pharmacologic agents are known to alter HDL levels. Studies show that patients with peptic ulcer disease treated with the H2-receptor antagonist cimetidine show significant elevations in their HDL, HDL2, and HDL3 profiles. In contrast, ranitidine has no effect, or may even decrease HDL levels. These divergent effects may be related to differences in pharmacologic activity unrelated to H2-receptor blockade. It should be noted that many of the variables affecting HDL levels were not controlled in these studies, and definite conclusions should not be extrapolated to the general population at risk for CHD. Currently, well-controlled trials to study the effect of cimetidine on HDL levels are in progress.

Effects of ranitidine and cimetidine on plasma lipoproteins in healthy subjects

Serum lipoproteins were monitored in 24 healthy subjects receiving either ranitidine or cimetidine for four weeks. Ranitidine produced a significant (P less than .05) reduction in high-density lipoprotein (HDL)-cholesterol in both men and women. Cimetidine caused a nonsignificant increase in HDL-cholesterol and a reduction in LDL-cholesterol that was significant (P less than .05) only in women. As these drugs had opposite effects on HDL-cholesterol levels, the mechanism of action is unlikely to be medicated by H2-receptor blockade.

Mast cell: its mediators and effects on arterial wall metabolism

Some general aspects of mast cells and their functional mediators, mainly histamine and heparin are reviewed. The actions of mast cells, histamine and heparin are analyzed in the context of their possible role in the physiology and pathophysiology of vascular tissue metabolism.

The effect of cimetidine and ranitidine on serum high density lipoprotein subfractions

Of the two major subfractions of high density lipoprotein (HDL), HDL2 cholesterol (HDL2-C) and not HDL3 cholesterol (HDL3-C) correlates negatively with coronary heart disease. To study the effect of cimetidine and ranitidine on HDL subfractions, 6 healthy males received cimetidine (600 mg bid) ranitidine (150 mg bid) and placebo (one tab bid) for 1 week each, in random order. Measurements of HDL cholesterol (HDL-C), HDL2-C, HDL3-C were made on day 7 of each week. Comparing cimetidine with placebo, HDL2-C/HDL-C, HDL2-C/total cholesterol and HDL2-C/HDL3-C increased significantly while HDL3-C/HDL-C decreased. There was no difference in HDL-C parameters between ranitidine and placebo. Cimetidine treatment results in redistribution of HDL subfractions in favour of HDL2. The mechanism is not H2-receptor antagonism as ranitidine had no such effect.

Chylomicronemia induced by cimetidine

A 35-yr-old man with moderate hypertriglyceridemia, associated with a positive family history for hyperlipidemia, developed chylomicronemia with abdominal pain, muscle pain, and splenomegaly while being treated with cimetidine for a duodenal ulcer. The chylomicronemia and the pain subsided after the drug was stopped. When the patient was rechallenged with the drug 6 mo later, the chylomicronemia reappeared after a treatment period of 6 days. Chylomicronemia and its complications should therefore be considered as a potential risk when cimetidine is prescribed to patients with known hyperlipidemia.

Cimetidine increases HDL-cholesterol, particularly in the HDL3 subfraction

Changes in high-density lipoprotein (HDL) cholesterol levels were monitored in five patients treated with cimetidine for gastrointestinal disturbances. A progressive rise of HDL cholesterolemia, statistically significant after four weeks of treatment and highly so after eight weeks (+ 25.4%) was noted. The composition of HDL2 varied insignificantly, whereas a marked rise of HDL3 cholesterol (+ 23.4%) and protein (+ 13.9%) was observed at the end of eight weeks. Cimetidine seems to act in a similar way as microsomal enzyme inducers, in spite of the described inhibition of specific pathways in drug metabolism; recent evidence shows that cytochrome P-450 turnover is delayed after cimetidine. Whatever the mechanism(s), H2 receptors may play a role in the cholesterol removal from tissues.

The influence of cimetidine and ranitidine on the plasma lipid pattern

The influence of H2-receptor antagonist drugs on the plasma lipid pattern has been studied prospectively in 51 patients treated with cimetidine (26 patients) or ranitidine (25 patients) for gastroenterological diseases. Total and HDL cholesterol and total triglycerides have been measured. Ranitidine did not influence the investigated parameters, while cimetidine produced a significant increase in the HDL cholesterol serum concentration (P = 0.008).

Effects of cimetidine and ranitidine on high density lipoprotein cholesterol concentrations

To assess the effect of cimetidine and ranitidine on high density lipoprotein (HDL) cholesterol concentration two groups of eight patients with duodenal ulcer or oesophagitis matched for age, sex, and cigarette consumption were given either cimetidine 1 g daily or ranitidine 300 mg daily for one month. There was no significant change in the cholesterol content of HDL and its subfraction HDL3 after treatment with ranitidine or cimetidine, or in the cholesterol content of the subfraction HDL2 after treatment with ranitidine; the HDL2 cholesterol concentration was, however, significantly increased after treatment with cimetidine. Further studies are being undertaken to establish the mechanism of this effect.