Effect of fenoldopam, a dopamine D-1 receptor agonist, on pituitary, gonadal and thyroid hormone secretion

Correlation between attention-deficit/hyperactivity disorder, its pharmacotherapy and thyroid dysfunction: A nationwide population-based study in Taiwan

OBJECTIVE

The aim of this study was to examine the comorbid rates of thyroid dysfunction among patients with attention-deficit/hyperactivity disorder (ADHD) and the general population. We further examined whether pharmacotherapy affects ADHD patients' risk of developing thyroid dysfunction.

DESIGN AND MEASUREMENT

We recruited 75 247 newly diagnosed ADHD patient and 75 247 healthy controls between January 1999 and December 2011 from the National Health Insurance database in Taiwan. We compared hyperthyroidism, hypothyroidism and other common paediatric psychiatric diseases between ADHD patients and controls. We carried out logistic regression analysis to identify an independent factor for predicting thyroid dysfunction. Furthermore, we analysed the time sequence of the diagnosis and the risk of developing a thyroid disorder after receiving pharmacotherapy.

RESULTS

Compared to the control group, the ADHD group had higher comorbidity rates of both hyperthyroidism (1.1% of ADHD vs 0.7% of controls, aOR: 1.72, P < 0.001) and hypothyroidism (0.6% of ADHD vs 0.2% of controls, aOR: 2.23, P < 0.001). Of the ADHD patients with comorbid thyroid dysfunction, about two-thirds and half of patients were diagnosed with ADHD prior to their diagnosis of hyperthyroidism and hypothyroidism, respectively. Furthermore, pharmacotherapy had no significant influence on the risk of developing hyperthyroidism (aHR: 1.09, P = 0.363) or hypothyroidism (aHR: 0.95, P = 0.719) among ADHD patients.

CONCLUSION

Patients with ADHD had greater comorbid rates with thyroid dysfunction than the control subjects, but pharmacotherapy for treating ADHD did not affect thyroid dysfunction later in life. However, these findings should be further verified using a clinical cohort with comprehensive laboratory assessment in future.

Lack of effect of the dopamine D1 antagonist, NNC 01-0687, on unstimulated and stimulated release of anterior pituitary hormones in males

Dopamine in humans inhibits the secretion of luteinizing hormone (LH), follicular stimulating hormone (FSH), thyroid stimulating hormone (TSH) and prolactin (PRL), and is a stimulator of growth hormone (GH) secretion. Dopamine-D1 receptor stimulation with fenoldopam increases basal PRL levels, suppresses TSH, and increases gonadotropin releasing hormone (LHRH) induced LH release. We have investigated the effect of a dopamine D1-receptor antagonist, NNC 01-0687, on the secretion of anterior pituitary hormones. In 8 healthy males NNC 01-0687 and placebo were administered orally in a double-blind placebo controlled cross-over study for three days with a wash-out period of 14 days. Hormonal responses (PRL, LH, FSH, GH, TSH, thyroid hormones and testosterone), unstimulated and LHRH/TRH stimulated, were studied on days 1 and 3. No significant difference (p > 0.05) between placebo and active periods was found neither in unstimulated nor in stimulated hormone concentrations expressed in absolute values, percent change of before, incremental values and area under the curve. These results suggest that the neuronal DA-D1 activity is not activated during basal conditions in healthy male subjects.

Fenoldopam: a new dopamine agonist for the treatment of hypertensive urgencies and emergencies

Fenoldopam is a selective dopamine agonist that is being considered for the parenteral treatment of systemic hypertension. In both an oral and parenteral form, the drug causes peripheral vasodilation by stimulating dopamine-1 adrenergic receptors. Its pharmaco-dynamics are reviewed in this article, along with the clinical experiences in patients with hypertensive urgencies and emergencies. Intravenous fenoldopam may provide advantages over sodium nitroprusside because it can induce both a diuresis and natriuresis, is not light sensitive, and is not associated with cyanide toxicity. There is no evidence for rebound hypertension after discontinuation of fenoldopam influsion.

Perinatal delta(9)-tetrahydrocannabinol exposure alters the responsiveness of hypothalamic dopaminergic neurons to dopamine-acting drugs in adult rats

We have recently reported that perinatal cannabinoid exposure altered the normal development of dopaminergic neurons in the medial basal hypothalamus at early postnatal and peripubertal ages. Most of these effects tended to disappear in adulthood, although we suspect the existence of a persistent, but possibly silent, alteration in the adult activity of these neurons. To further explore this possibility, we evaluated the responsiveness of these neurons to pharmacological challenges with a variety of dopaminergic drugs administered to adult male and female rats that had been exposed to delta(9)-tetrahydrocannabinol (delta(9)-THC) or vehicle during the perinatal period. In the first experiment, we evaluated the sensitivity of hypothalamic dopaminergic neurons to amphetamine (AMPH), which causes enhancement of dopaminergic activity by a variety of mechanisms. The most interesting observation was that both adult males and females, when perinatally exposed to delta(9)-THC, showed a more marked AMPH-induced decrease in the production of L-3,4-dihydroxyphenylacetic acid (DOPAC), the main intraneuronal metabolite of dopamine (DA), although this did not affect the prolactin (PRL) release. In the second experiment, we evaluated the in vivo synthesis of DA by analyzing the magnitude of L-3,4-dihydroxyphenylalanine (L-DOPA) accumulation caused by the blockade of L-DOPA decarboxylase with NSD 1015. As expected, NSD 1015 increased L-DOPA accumulation and decreased DOPAC production, with a parallel increase in PRL release, all of similar magnitude in both delta(9)-THC- and oil-exposed adult animals. In the last experiment, we tested the magnitude of the increase in PRL release produced by the administration of either SKF 38393, a specific D1 agonist, or sulpiride, a specific D2 antagonist. Both compounds increased plasma PRL levels in adult animals of both sexes, the effects in females being significantly more marked. The perinatal exposure to delta(9)-THC also modified the degree of increase in plasma PRL levels induced by both compounds, with opposite responses as a function of sex. Thus, delta(9)-THC-exposed females responded more intensely to SKF 38393 and, particularly, to sulpiride than oil-exposed females, whereas delta(9)-THC-exposed males responded to SKF 38393 lesser than oil-exposed males, although both responded equally to sulpiride. In summary, our results are consistent with the possible existence of subtle changes in the activity of hypothalamic dopaminergic neurons in adulthood caused by the exposure to delta(9)-THC during perinatal development. These silent changes could be revealed after the administration of drugs such as: (i) AMPH, whose effect producing a decreased DOPAC accumulation was more marked in delta(9)-THC-exposed males and females; and (ii) SKF 38393 and sulpiride, whose stimulatory effects on PRL secretion were of different magnitude in delta(9)-THC-exposed animals, with an evident sexual dimorphism in the response. The neurochemical basis for these differences remains to be determined.

Fenoldopam: a review of its pharmacodynamic and pharmacokinetic properties and intravenous clinical potential in the management of hypertensive urgencies and emergencies

Fenoldopam is a dopamine agonist that causes peripheral vasodilation via stimulation of dopamine 1 (D1) receptors. The efficacy of an intravenous infusion of fenoldopam in decreasing blood pressure in patients with a hypertensive urgency, including patients who developed hypertension after coronary artery bypass graft surgery, and in a small number of patients with hypertensive emergency, is similar to that of sodium nitroprusside. However, unlike sodium nitroprusside, fenoldopam also increases renal blood flow and causes diuresis and natriuresis. There is no evidence of rebound hypertension after stopping the infusion. As the tolerability profile of fenoldopam is generally similar to that of sodium nitroprusside, fenoldopam appears to be an effective alternative to sodium nitroprusside in the immediate treatment of patients who develop severe hypertension and in whom oral treatment is not practical. Fenoldopam may be particularly useful in patients who develop hypertension after coronary artery bypass graft surgery, but further studies are required to confirm its role in hypertensive emergency.

Identification of a D1 dopamine receptor, not linked to adenylate cyclase, on lactotroph cells

1. We studied the lactotroph cells of the rat by both in vivo and in vitro pharmacological techniques for the presence of D1-receptors. Both approaches revealed the presence of D2-receptor, stimulated by quinpirole (resulting in an inhibition of prolactin secretion) and blocked by domperidone. 2. Administration of fenoldopam, the most selective D1-receptor agonist currently available, resulted in a dose-dependent decrease of prolactin secretion in vivo (after pretreatment with alpha-methyl-p-tyrosine) and in vitro (cultured pituitary cells). This increase was dose-dependently blocked by the selective D1-receptor antagonist, SCH 23390, and although the effect of fenoldopam was less than that obtained by D2-receptor stimulation, these data suggest that a D1-receptor also controls prolactin secretion. 3. In order to detect the location of these dopamine receptors, autoradiographic studies were performed by use of [3H]-SCH 23390 and [3H]-spiperone as markers for D1- and D2-receptors, respectively. Specific binding sites for [3H]-SCH 23390 were demonstrated. Fenoldopam dose-dependently reduced [3H]-SCH 23390 binding, but had no effect on [3H]-spiperone binding. Immunocytochemical labelling of prolactin cells after incubation with [3H]-SCH 23390 revealed that the granulae and hence, D1 binding sites were present on the lactotroph cells. 4. Radioligand binding studies performed on membranes from anterior pituitary cells revealed the presence of the D2-receptor (54 fmol mg-1 protein) with a Kd of 0.58 nM for [3H]-spiperone, but failed to detect D1-receptors. 5. Finally, we studied the effect of dopamine and of fenoldopam on the adenosine 3':5'-cyclic monophosphate (cyclic AMP) content of anterior pituitary cells. Although cyclic AMP increased upon prostacyclin administration, indicating an intact adenylate cyclase system, fenoldopam failed to increase the cyclic AMP production. 6. It is tempting to speculate that fenoldopam reduces prolactin secretion through interaction with a non-cyclase-linked D1-receptor on the lactotroph cells.

Pulsatile gonadotropin secretion and basal prolactin levels during dopamine D-1 receptor stimulation in normal women

The effect of the specific dopamine D-1 receptor agonist Fenoldopam on pulsatile gonadotropin secretion and prolactin (PRL) secretion was investigated in normal women. The gonadotropin response to subsequent gonadotropin-releasing-hormone (GnRH) administration was also studied. Eight women received 8-hour infusions of either Fenoldopam (0.5 microgram/kg per minute) (Smith Kline and French, Harrow, United Kingdom) or placebo. After 7 hours of infusion, GnRH was given intravenously. The luteinizing hormone (LH) response to GnRH was significantly higher during Fenoldopam compared with placebo (LH; 13.1 +/- 9.0 versus 9.4 +/- 4.3 IU/L). Basal LH levels, pulse amplitude, and pulse frequency during Fenoldopam infusion were not different from placebo. Prolactin levels increased significantly during Fenoldopam (24 +/- 2 micrograms/L) compared with placebo (16 +/- 2). The results suggest that D-1 receptor stimulation does not affect pulsatile gonadotropin secretion but increases the pituitary responsiveness to GnRH. Additionally, dopamine and Fenoldopam have opposite effects on PRL secretion, the latter increasing PRL levels.

Dopaminergic inhibition of glycoprotein hormone alpha-subunit in normal subjects

The pituitary glycoprotein hormones thyrotropin (TSH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH) consist of two noncovalently linked subunits, alpha and beta. In addition to producing intact hormone, the pituitary releases free alpha-subunit, which is stimulated by gonadotropin-releasing hormone (GnRH) and thyrotropin-releasing hormone (TRH). However, little is known about the dopaminergic regulation of free alpha-subunit in vivo. The effect of dopamine (DA), metoclopramide (MTC), and the specific DA D-1 receptor agonist, fenoldopam, on circulating alpha-subunit levels was studied in normal men and women. Normal women received 4-hour infusions of either glucose (n = 6) or DA at rates of 0.04 (n = 6), 0.4 (n = 6), and 4.0 micrograms/kg.min (n = 6). After 3 hours, 10 mg MTC was administered intravenously (IV). The high dose of DA significantly lowered alpha-subunit levels (P less than .05). No response to MTC was observed in any of the groups. Six women received glucose or DA infusion (4.0 micrograms/kg.min) for 18 hours. DA significantly reduced basal alpha-subunit levels compared with control infusion (P less than .05). MTC administration after 17 hours induced a significant increase in alpha-subunit levels on the day of DA infusion compared with control (P less than .05). In a third study, nine normal males received fenoldopam (0.5 microgram/kg.min) or placebo infusions for 4 hours. Fenoldopam did not affect basal alpha-subunit levels, but the alpha-subunit response to a GnRH/TRH bolus was significantly increased during fenoldopam compared with control (P less than .05). The results suggest that alpha-subunit release may be modulated by the dopaminergic system in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dopamine and a dopamine D-1 receptor agonist on pulsatile thyrotrophin secretion in normal women

The inhibitory effect of a pharmacological dose of dopamine and the specific dopamine D-1 receptor agonist fenoldopam on basal and pulsatile TSH secretion was investigated in normal women. The TSH response to fenoldopam and subsequent releasing hormone administration was also studied. Six women received placebo or dopamine infusion (4.0 micrograms/kg min) for 17 h. After 9 h, blood samples were collected every 10 min between 0800 and 1600 h for measurement of TSH. Eight women received 8-h (0900-1700 h) infusions of either fenoldopam (0.5 micrograms/kg min) or placebo. After 7 h of infusion 10 micrograms TRH, 5 micrograms GnRH and 25 micrograms CRF was given i.v. Blood samples were collected every 10 min. Dopamine infusion as well as fenoldopam infusion significantly reduced both mean basal TSH secretion and TSH pulse frequency compared with corresponding control infusions (P less than 0.05). However, while the effect on TSH pulsatility was comparable (P greater than 0.05), the percentage decrease in basal TSH levels after 16 h of dopamine infusion was 51 +/- 16% (mean +/- SD) and after 7 h of fenoldopam infusion 19 +/- 12% (P less than 0.05). Neither of the drugs affected TSH pulse amplitude and fenoldopam did not influence TRH-stimulated TSH release (P greater than 0.05). The results suggest that dopamine D-1 receptors are involved in modulation of TSH pulsatility probably at the hypothalamic level. It is argued that dopaminergic inhibition of basal TSH secretion and TSH pulsatility is predominantly regulated through dopamine D-2 receptors at the pituitary level, and through D-1 receptors at the hypothalamic level, respectively.