The pituitary inhibitory system: its role in pain perception

The present study was designed to investigate the pain relief mechanism of electrical stimulation to the pituitary and the relationship between hypothalamic and pituitary analgesic mechanism through the observation of monkey behavior and characteristics of tooth pulp-evoked potentials. The results suggest that pituitary-stimulating analgesia should be differentiated from hypothalamic-stimulating effect. In view of the facts, the theory of the Pituitary Inhibitory System is proposed.

Electrophysiologic evidence for involvement of the pituitary region in opiate analgesia

In the past, various reports have discussed the relationship between the pituitary and analgesia. The purpose of the present study was to explore the possible role of the pituitary region in the mediation of pain by opioids. Tooth pulp evoked potentials recorded from primary somatosensory cortex and from the pituitary region of rabbits were recorded before and after an injection of opiates. Tooth pulp evoked potentials recorded from the primary somatosensory cortex were markedly inhibited after admission of fentanyl, while the tooth pulp evoked potentials recorded from the pituitary region were facilitated. It is concluded that the pituitary region plays a role in the mediation of pain and that this area is involved in the mechanism of opiate analgesia.

Relief of cancer pain in man: alcohol-induced neuroadenolysis vs. electrical stimulation of the pituitary gland

To explore new methods for the control of intractable pain caused by advanced cancer, the analgesic effect of electrical stimulation of the pituitary gland was investigated in 25 patients. The results were compared with a control study and with the effects of alcohol-induced pituitary neuroadenolysis (NALP) in the same patients. The pain score (0: no pain at all, 4: extreme pain) in the control study was 3.88 +/- 0.33. After electrical stimulation of the pituitary gland it was 1.24 +/- 1.61; and after NALP it was 1.0 +/- 1.60. The pain scores after electrical stimulation and NALP were significantly lower (P less than 0.01) than those in the control study; but there was no significant difference when the two were compared with each other. The duration of pain relief following NALP (59.65 +/- 68.72 days) was significantly longer compared with that recorded following electrical stimulation (2.97 +/- 2.58 days). Autopsy examinations of 3 patients who expired from their malignancies revealed that the pain relief was unrelated to the degree of necrosis induced in the pituitary by alcohol. Naloxone administration did not inhibit the analgesic effect of either NALP or electrical stimulation. The advantages and disadvantages of electrical stimulation, the pain relief mechanism activated by this method, and potential clinical applications are also discussed.

Mechanism of neuroadenolysis of the pituitary for cancer pain control

Several theories have been advanced to explain how neuroadenolysis of the pituitary (NALP) relieves cancer pain. Interference with hormonal regulation, interruption of pain pathways and a compensatory overproduction of brain endorphins have been proposed. The purpose of the present experimental study is to determine whether neuronal activity of the pituitary gland, as related to the primary somatosensory cortex (PSC), may be involved in the pain perception pathway influenced by NALP, using EEG and tooth pulp evoked potentials (TPEPs). Pituitary activity showed a high voltage slow activity which slowed after alcohol injection into the sella turcica. When naloxone was injected after NALP, a rhythmic high voltage activity appeared in the pituitary gland. After NALP, the TPEP recorded from the PSC disappeared, while NALP induced an increase in the amplitude of the TPEP in the pituitary gland. An injection of naloxone severely decreased this response in the pituitary gland, in contrast to changes in the PSC where the original response reappeared after an injection of naloxone. Our hypothesis is that an increase of TPEPs (hyperactivity) in the pituitary gland is produced after alcohol wounding (wounding effect), leading to a decrease of pain response in the sensory cortex (decrease of TPEPs). This wound effect may be influenced by endorphins, because naloxone, a specific antagonist of opiate receptors, reversed the changes in TPEPs in both places.

Respiratory distress and beta-endorphin-like immunoreactivity in humans

Beta-endorphin-like immunoreactivity was determined in the plasma of twenty patients suffering from hypoxia of various etiologies and in twenty healthy adult volunteers who served as controls. Mean beta-endorphin-like immunoreactivity in the hypoxic patients was 53.2 +/- 5.5 (SEM) pg/ml, as compared to the volunteer subjects in whom the mean level was 6.2 +/- 1.9 pg/ml (P less than 0.01). Significant negative correlations were present between both arterial pH (r = -0.85; P less than 0.01) and arterial PO2 (r = -0.80; P less than 0.01) and beta-endorphin-like immunoreactivity. These findings seem to lend support to the hypothesis that hypoxia and acidosis represent stressful conditions which may stimulate the release of beta-endorphin in humans.

Exposure of nitrous oxide to X-rays. Production of nitric oxide and nitrogen dioxide

X-radiation has been shown to produce nitric oxide (NO) and nitrogen dioxide (NO2) in the presence of nitrous oxide (N2O). The purpose of the present study was to confirm how much NO and NO2 was produced when constant amounts of nitrous oxide were exposed to constant X-radiation. Twenty polyethylene bottles (capacity 10 litres) were filled with nitrous oxide alone. Another 20 bottles were filled with nitrous oxide and 30% oxygen. Each bottle was placed at a distance of 30 cm from the X-ray tube and they were directly in the line of the X-ray beam at a setting of 90 kV at 0.5 mA, a standard setting for chest fluoroscopy. The range of duration of X-ray exposure was from 0 (control), to 2, 3, and 5 minutes in five bottles each, respectively. A colorimetric recording method (Saltzman) and a chemiluminescent monitor were used for measurement of NO and NO2. In the bottles filled with nitrous oxide alone, the production of NO was not affected by the duration of X-ray exposure, but the longer duration of X-ray exposure produced a larger amount of NO2. In the bottles filled with nitrous oxide and 30% oxygen, the longer duration of X-ray exposure produced larger amounts of both NO and NO2. These finding confirmed a previous investigation in which nitrous oxide was not inert under X-ray exposure. As the presence of oxygen plays an important role in the oxidation of nitrous oxide under X-ray, this study suggests another potentially hazardous interaction that may occur secondary to the administration of an anaesthetic in the presence of X-irradiation such as pulmonary angiography, cardiac catheterisation, and fluoroscopic bronchoscopy or biopsy.